Rework UI to split up library and project creation pages

[soundchaser128]

I think it no longer makes a lot of sense to have the library (video list) and music pages as part of the multi-step form to create a compilation. Idea for a new layout:

• /: Redirects to /library/video
• /library/video: Show list of videos with filtering, search etc. Clicking on a video gets you to /library/video/<id>, which is just the current marker edit/create page. Allows adding and removing videos as well. Batch editing planned for the future as well. (see #89)
• /library/markers: Show list of all markers, does not currently exist in this form. Could explore showing markers grouped by video, or just as a grid
• /library/music: List of songs, allows adding and removing songs.
• /library/performers: List of performers. Not yet implemented.
• /project/select-videos, /project/select-markers, /project/select-music, /project/video-options, /project/preview, /project/generate, /project/<id>/download and /project/<id>/funscript are the pages for the different parts of the project creation form.
• For the future, this would also make it easier to start a compilation based on different criteria than selected videos. Instead, you could select performers first, marker titles, video tags, or other criteria.
• /tv/start: ClipMash TV setup form
• /tv/watch: ClipMash TV

The basic layout I'm imagining for the library pages would be a navigation bar on top with links for each of the library pages, then a "New compilation" button somewhere prominent, and a link to the TV feature as well.