store choices for recent changes and diff views in cookie (FS#2438 and
FS#2700)

Note: These changes don't work yet. The cookie is not set and deletes the old
one.
fixed setting cookie not working
Fix set_doku_pref cookie date and value
urldecode DOKU_PREFS cookie values
removed urldecode from js again (it's already in init())
check preferences in cookie against urldecoded key
some urldecoding also needed in the cookie setter
update for encoded cookie value & using rawurlencode
ensure getter works with keys & values containing '#'
Merge pull request #164 from splitbrain/diff_recent_prefs

store choices for recent changes and diff views in cookie