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.
docs: clarify support for {=PRICE] syntax
Merge remote-tracking branch 'remotes/xinruo/select2'
fix a compilation warning
web: loosen "starting web browser" message for servers
web: don't show prices in the accounts sidebar (fixes #114)
parsing: don't fail when a csv amount has trailing whitespace (fixes #113)
parsing: update a csv reader error message
parsing: make balance assertions more robust with different precisions (#119)

Also note another issue.