Remove IDE generated files from git

[hrodrick]

In the repository are some files which were auto-generated by Android Studio (or another tool) and sometimes they change based on user configuration or IDE version.

These values and their updates can cause merge conflicts or lead to unexpected errors on some user machines, so to avoid them we need to verify which auto generated files are being tracked in Git and remove them, after that we need to add the corresponding rules into the .gitignore file

Based on the comment by @marcossalto in https://github.com/rootstrap/android-base/pull/51#discussion_r746616113