webui: Improve webui

Use %h3.page-header and new sections.
webui: Fix adding new mount

For some reason, a wrong variable name was kept.
webui: Move remove button at end of mount
webui: Insert new mounts after creation form

This is better as people can keep adding new mounts without moving in
the page, and it fixes a weird bug where mounts where displayed multiple
times.
Merge pull request #1 from vuntz/webui

Several webui fixes