Sentry gradle script refactoring, compatibility with Gradle 5.0 recovered

[OleksandrKucherenko]

Refactoring:

• sentry cleanup tasks are injected into main clean tasks calls graph. benefits:

1. cleanup happens when its really forced by user;
2. caching for upload task will start working; no modifications to input files will be treated by gradle as ability to skip task execution and win us several seconds;

• logs of the tasks are printed only when gradle --info flag is provided
• tasks connected to each other now via call graph
• simplified names of the tasks, bundle task name itself already contains flavor and build type. No need to repeat that
• tasks declared in our logical group now sentry.io, ./gradlew tasks will display them properly now

resolved issues: #520 and #519

[OleksandrKucherenko]

Upload Task in execution graph:

Cleanup Tasks in execution graph:

[OleksandrKucherenko]

Sentry tasks group:

[OleksandrKucherenko]

@HazAT please review and merge. Will be great to have a gradle 5.0 fix in master

[HazAT]

Hey, thanks for the PR, it looks solid, I still need to test it.
Could you please resolve the merge confilict (a PR has been merged that fixed Windows support).

After that I will happily merge the changes.

[OleksandrKucherenko]

@HazAT - I rebase the PR and merge all the changes. Should be fine now to merge

[HazAT]

Perfect, thank you very much! 🥇