gradle: move general configuration to top-level build.gradle
gradle: use latest version of the support library (13.0.0 -> 19.0.+)
gradle: use latest version of the build tools (18.0.1 -> 18.1.1)
UI: implement Cards-style interface for plugin lists (squashed commits)

This is a combination of 5 commits.
The first commit's message is:
UI: use card-style interface for the plugins list

This is the 2nd commit message:
Some UI tweaks

This is the 3rd commit message:
Cards UI: add dark theme and integrate it with the settings

This is the 4th commit message:
Cards UI: implement for the MITM section

This is the 5th commit message:
Cards UI: cosmetic changes