[webmail] ability to sort emails

[tonio]

In the emails listing, we need the possibility to sort emails (on date/sender/etc.) by clicking on columns.

The IMAP protocol provides a way to filter searchs.

[tonio]

Almost done in [87a0409582f7].

The problem is that we lost the search criterion when location.hash is modified. We need to implement a kind of URL object to wrap all accesses to location.hash... For example, it would be nice to have something like :

hash.baseurl("somewhere")

hash.add_argument("arg", "value")
hash.mod_argument("arg", "newvalue")
hash.del_argument("arg")

[tonio]

First good version in [60c2b603294e]. It needs some testing now...