New ‘Edit’ icons.
Send the activity context so WPHtml has the proper context reference.
Fixes #450. Seemed like a simple fix but I ran into a bunch of problems. Here’s a summary of the changes:

 * WPImageSpan appeared to be storing the exact same data as the MediaFile class. So I simply added a MediaFile instance to WPImageSpan and removed all of the places in code where the WPImageSpan data was copied over to the MediaFile.
 * Changed saveMediaFile() in wpDB to also update the media file db row if it already exists.
 * Fixed some naming conventions.
 * Changed WPImageSpan thumbnail to be larger in the post editor. Looks nice!
 * If a WPImageSpan is in the post editor, it will have an edit icon drawn in the lower-right corner to clue in the user that they can tap it to edit the image’s options.
* Removed some duplicated code related to creating image thumbnails.
Fixes media upload by using MediaFile.filePath instead of fileName. Cleaned up some code in PostUploadService.
Don’t show the edit icon if the MediaFile is a video.
Merge branch 'develop' into issue/450-editor-media-fixes
Fixes issue where new pictures added to existing posts were not saving.
Correcting placement of code, shouldn’t be in the for loop.
Fixed db update method to pass the selection arguments (face palm)
Simplified savePostContent() method.
Save existing post content even if we have no images in the post.
Create a separate Editable object instead of using the one from the post content EditText. Fixes issue where you’d see a split second of HTML as the post was saved or published.
Only show the edit icon on a WPImageSpan if it is in the editor fragment.
Fixing issue where changes to MediaFiles were not saving.
Fixing up some of the issues reported by @nbradbury here:

https://github.com/wordpress-mobile/WordPress-Android/commit/c531bbec313a43936145fe43e41031a872c2d276#commitcomment-4873772
https://github.com/wordpress-mobile/WordPress-Android/commit/c531bbec313a43936145fe43e41031a872c2d276#commitcomment-4873961
https://github.com/wordpress-mobile/WordPress-Android/commit/c531bbec313a43936145fe43e41031a872c2d276#commitcomment-4874096
https://github.com/wordpress-mobile/WordPress-Android/commit/c531bbec313a43936145fe43e41031a872c2d276#commitcomment-4874138
Merge pull request #471 from wordpress-mobile/issue/450-editor-media-fixes

Issue/450 editor media fixes