Multiple improvements

1) Fix "Bad Request" when changing avatar directory in tl_settings (#2)

2) Make the insert tag more dynamic with query parameters.
`{{avatar[::id][?width=X&height=Y&mode=M&alt=ALT&class=CLASS]}}`
**width** The width of the avatar.
**height** The height of the avatar.
**mode** The resize mode.
**alt** [default=##firstname## ##lastname##] The ALT text, overwrites the default alt text.
**title** [default=] The TITLE text, overwrites the default title text.
**class** [default=avatar] The css CLASS'es, overwrites the default css classes.

3) Make possible to automatic resize images on upload. (=> configurable in system settings).

4) Make more configurable.
* Define default ALT text in system settings.
* Define anonymous ALT text in system settings.
* Define default TITLE text in system settings.
* Define anonymous TITLE text in system settings.
* Define default css CLASSes in system settings.
* Define anonymous css CLASSes in system settings.
ALT and TITLE now allow simple tokens.

5) Improve the code.