Revert "unfiltered display of preview"

This reverts commit 54502968799e58fe6567ab1c3d5cd81967a5cf7c.
I don't know, why the code was changed before, but that caused, that images
in menu weren't transparent, for example image of favourites in
the serverbrowser.
keep the last five versions of saved.cfg and init.cfg

Renames the existing saved.cfg to saved-old-1.cfg (and an existing -1 to
-2, and so on) before the new saved.cfg is written.

This should help in cases where players mess up their config, because the
config is deleted with a five-game-starts delay.
Fix gonext command and do it random

Commit fixes broken "gonext" command, among other things reading time
from maprot, and it does random result of this command.
It also removes get_next() function, because it messes up the maprot,
so shouldn't be used.
Add alternative views in serverbrowser and improve favourites

Alternative views in the serverbrowser are implemented with use favourites.
Categories (names) of favourite servers, which will be displayed on the
views, have to be included in "serverbrowseraltviews" alias (accessible
in menu).
Switching between views is possible with use Alt + Mouse wheel and
Alt + Up/Down (or eventually "[" and "]", if they are dedicated keys
on your keyboard).

The commit also:
1. adds MATCH category to favourites;
2. shows category name in settings of favourites;
3. shows weights in serverbrowser instead of favourites image,
when showweights = 1;
4. cleans up some tabs.
fix filtering of serverdescriptions for ascii scores