Edit existing shreds and stuff:
 * comments for future refactoring, refs #53
 * new http endpoint to edit/save already tagged shred, refs #51
 * shred direction stuff refactored: new field added to ShredTags, degree renamed to angle
 * templates renamed according to a new scheme: all partials/ajax responses/macros now prefixed with underscore
 * summarized_tags field removed from Shreds
 * list of base tags adjusted
 * JS code slightly refactored and updated to make it possible to edit shreds and reuse existing code
 * Bug in jScroll.js fixed
 * Edit functionality is now done, fixes #24
Clarification on bugfix for jscroll