Upgrade gradle, update dependencies and cache circleci builds

[cal-pratt]

This PR builds on top of #274 and should be reviewed after that has been merged.

Circle CI now caches the gradle version and the downloaded gradle dependencies between builds. This ends up saving about a minute of build time (reduced from 3:30 to 2:30 🎉 ). If we ever go to remove dependencies from the project, there is an option in the build page to re-build the project without a cache. This will make circle ci create a brand new cache for subsequent builds.

The version of gradle was updated to 3.4 to fix #268 . The compiler warning about the deprecated Constructor DefaultSourceDirectorySet was solved when updating the project dependencies. Updating this dependencies did however deprecate some of the features that we use in these libraries. Most changes were simple apart from the deprecation of Observable#create. I use this method often when I have to poll from a source, so I'll have to get used to creating the sequence in other ways. In our case it was being used by the joystick code. I was able to rearrange it to not use create. Will need to test on the joystick before we push.

[cal-pratt]

@ConnorWhalen This PR just became critical.

Looks like Gradle 2.14 has been removed from the Personal Package Archives (PPA) ppa:cwchien/gradle. This means that we can't run any of the CCI builds, or use the captain playbook until this PR gets merged.

[cal-pratt]

From the CCI logs:

$ sudo apt-get install gradle-2.14
Reading package lists... Done


Building dependency tree       


Reading state information... Done

E: Unable to locate package gradle-2.14
E: Couldn't find any package by regex 'gradle-2.14'

sudo apt-get install gradle-2.14 returned exit code 100

Action failed: sudo apt-get install gradle-2.14

From vagrant console:

ubuntu@ubuntu-xenial:~$ sudo add-apt-repository -y ppa:cwchien/gradle
gpg: keyring `/tmp/tmpqu85idb1/secring.gpg' created
gpg: keyring `/tmp/tmpqu85idb1/pubring.gpg' created
gpg: requesting key 9D06AF36 from hkp server keyserver.ubuntu.com
gpg: /tmp/tmpqu85idb1/trustdb.gpg: trustdb created
gpg: key 9D06AF36: public key "Launchpad PPA for Cheng-Wei Chien" imported
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)
OK
ubuntu@ubuntu-xenial:~$ sudo apt-get update
Hit:1 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:2 http://ppa.launchpad.net/ansible/ansible/ubuntu xenial InRelease
Hit:3 http://archive.ubuntu.com/ubuntu xenial InRelease
Hit:4 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Get:5 http://ppa.launchpad.net/cwchien/gradle/ubuntu xenial InRelease [17.5 kB]
Hit:6 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Get:7 http://ppa.launchpad.net/cwchien/gradle/ubuntu xenial/main amd64 Packages [1,436 B]
Get:8 http://ppa.launchpad.net/cwchien/gradle/ubuntu xenial/main Translation-en [964 B]
Fetched 19.9 kB in 1s (18.5 kB/s)
Reading package lists... Done
ubuntu@ubuntu-xenial:~$ sudo apt-get install gradle-2.14
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package gradle-2.14
E: Couldn't find any package by glob 'gradle-2.14'
E: Couldn't find any package by regex 'gradle-2.14'
ubuntu@ubuntu-xenial:~$

[ConnorWhalen]

Changes look good and I was able to cleanly run the captain playbook and build using gradle 3.4 👍