Add progress report for media uploading.

Use NSProgress to report uploading progress.
Add NSProgress to interface of MediaService.
Fix error callback calls and make them use current queue instead of main one.
Improved documentation of MediaService.
Add progress reporting for setting featured image.
Only increase size by 1 to avoid show incorrect size of file.
Add progress reporting view controller to legacy editor.
Replace cancel button for done button.
Add a progress view on navbar to show progress on uploading media.
Improve progress reporting by only incrementing when all file is completed.
Fix progress report in XMLRPC code.
Improve progress report and allow to stop single uploads.
Add a cancel all button for media upload.
Show cancelled state.
Merge branch 'develop' into feature/ProgressOnMedia

Conflicts:
	Podfile
	WordPress/Classes/ViewRelated/Post/WPLegacyEditPostViewController.m
	WordPress/Classes/ViewRelated/Post/WPPostViewController.m
	WordPress/WordPress.xcodeproj/project.pbxproj
Merge branch 'develop' into feature/ProgressOnMedia
Fix project file.
Update pods.
Update pods.
Show progress on each image.
Add and remove progress view from navbar on appear and disappear.