WLocalDateTime: remove const qualifier from return type of time() and date()

WLocalDateTime::time() and WLocalDateTime::date() return by value,
not by reference, so const qualifier of return type is useless.
add possibility to use external TinyMCE (e.g., CDN), add option tinyMCEURL

If configuration option tinyMCEURL is specified, options
tinyMCEBaseURL and tinyMCEVersion are ignored.

Probably, we need a possibility to specify custom URLs for
langs and plugins (TinyMCE 4 options external_plugins and language_url).
fix documentation of WTextEdit

\ref xxx "yyy
zzz"
results in disrupted text of anchor:

see <a>configuration</a>properties".

So, anchor text should be written in a row.
Dbo.UserDatabase: maxAuthTokensPerUser's accessors

see #1763 http://redmine.emweb.be/issues/1763
Dbo.UserDatabase: remove old token if too many

close #1763 http://redmine.emweb.be/issues/1763
Merge pull request #39 from starius/master

several improvements; I like!