Update all dependencies to latest stable versions

All:
- Gradle version: 2.1 to 2.2.1 (required for Android Studio 1.0 RC2)
- Gradle plugin: 0.14.1 to 0.14.4
- Build tools: 21.1 to 21.1.1

Main:
- okhttp:1.2.1 to okhttp:2.1.0 and okhttp-urlconnection:2.1.0
- picasso:2.1.1 to picasso:2.4.0
- eventbus:2.2.0 to eventbus:2.4.0
- support-v4:21.0.0 is transitively added via appcompat, removed from build.gradle
- appcompat-v7:21.+ to appcompat-v7:21.0.2
- recyclerview-v7:21.+ to recyclerview-v7:21.0.2

example-source-500px:
- retrofit:1.7.1 to retrofit:1.8.0

provider:
- Reordering build.gradle to match others

wearable:
- Reordering build.gradle to match others
Merge pull request #101 from ianhanniballake/dependency_update

Update all dependencies to latest stable versions