Attachment improvements

This requires !1392 (merged) due to refactoring done in there

User-facing changes

0. Attachments now are always in same order as uploaded
1. Attachments in post-status-form and in post are uniform now.
2. You can now watch videos in media-modal even if you disabled that option (via zoom icon)
   
3. You can now watch flash in media-modal (takes up entire screen tho)
4. File/image descriptions are pre-filled if your instance prefills descriptions for you
   
5. New button that indicates that attachment has a description, clicking it toggles a preview of description
   
   
6. Notifications about favorites/repeats take up less space
   
7. Too many attachments are truncated
   
8. Display full description in media-modal
   
   
9. Ability to rearrange attachments when making a post, no drag-n-drop yet.
   
10. Attachments counter
    
11. Proper indication that next image is loading when you press left/right
    

Technical

• Gallery now handles all attachment business, period. No more "non-gallery attachments"
• Attachments now can have edit, remove, move up and down functions for post-status-form
• Refactored related parts
• Some improvements to flash component, namely - no longer has its own button for stopping, instead button now is in Attachment component.