web: use select2 to autocomplete

Use the javascript library select2 to autocomplete descriptions and
account names when adding a transaction. The autocomplete searches by
substring, prefix and infix. New values will also be accepted.

This replaces dhtmlxcombo library so it is removed. Also updated jquery
to the latest 1.10.1.
Merge remote-tracking branch 'remotes/xinruo/select2'
fix a compilation warning