Adds handling for gif and png images when uploading to the WP media library. Fixes #548 and #84.
Merge branch 'develop' into issue/548-gif-support

Conflicts:
	src/org/wordpress/android/util/PostUploadService.java
Code cleanup.
Merge pull request #551 from wordpress-mobile/issue/548-gif-support

Adds support for uploading images in gif and png image formats.