Avoid page reload when triggering actions in bookmark list

[sissbruecker]

Changes the bookmark list and tag cloud to be updated in place, rather than reloading the full page, when an action like archive, delete or a bulk edit is triggered. This improves the UX:

• The scroll position of the page doesn't reset anymore, making it easier to work with bookmarks at the end of the list
• The bulk edit bar now stays open and keeps its state (e.g. tag names), making multiple bulk edits in a row easier

Technically this adds Javascript that cancels the form submission, posts the form programmatically, and then loads and replaces the updated HTML for the list and tag cloud. Actions that trigger navigation to a new URL (doing a search, filtering for tags, using pagination) still result in a full reload.