Added Ivanhoe Move Source

For new moves, added a field to pull and save the ID of the move to which the
current move responds.
Added buttons, made Make a Move button float right.
added basic loop to single move display
added working code to display the linked title of the source post of a move if it has a source post
added new query and loop to pull posts that respond to a given post. Displays the same posts on all move pages now regardless of whether they have responses
Changes back to meta_value.
Formatting and test cleanup.
Created single button class, make-a-move id, changed color of links for button class
Displays excerpts of moves

Single Ivanhoe Move page now display excerpts of moves instead of entire
move content.
Added subtlety to links
Merge branch 'feature/related_moves' of github.com:scholarslab/ivanhoe into feature/related_moves
Pagination for moves on individual game pages

10 moves are displayed per page on single ivanhoe games.
Updates move pagination to work with pretty URLs.

Pagination for the moves list on single Ivanhoe games should now work with both
pretty URLs and the default URLs. This adds a rewrite rule to account for the
page query variable, and overrides WordPress's default URL redirection so the
/page/[num] remains in the URL when clicking pagination links.