Clean up Utils

Put most util functions in a single class.

When checking for empty text, we'll trim it as well as a last check.
e.g. now "  " will be detected as empty as well.

Stop using hardcoded strings for permissions and features, and use the
SDK constants instead.
Use Build.SERIAL directly
Use isNullOrEmpty in more places
Export versionName instead of manually updating it with each release.
Tests for Utils
Merge pull request #59 from segmentio/f2prateek/clean-up-utils

Clean up Utils