Update compileSdkVersion to 21 and Gradle Android Plugin to 1.0.0
Add code style settings for Android Studio
Remove Eclipse settings
Use TextUtils.isEmpty
Package visibility
Move database code into correct package
Package visibility
Fix visibility
Fix visibility
Removed useless line
Remove K9FragmentActivity

Because it's same with K9Activity now, no need to keep it.

Test Plan:
./gradlew installDebug, and test the MessageList activity
Merge pull request #518 from frankdu/clean-up

Remove K9FragmentActivity
Merge pull request #517 from pylerSM/patch-1

Removed useless line