Optimize and fix autodownload feature

The commit:
1. fixes value of download speed in KB;
2. introduces unique names of progress_callback() functions;
3. removes one unnecessary write_callback() function;
4. removes duplicated code/info in loadmodel().
Add altering pages in serverbrowser and improve favourites

Altering pages in serverbrowser are implemented with use favourites.
Categories (names) of favourite servers, which will be displayed on the
pages, have to be included in "serverbrowseraltpages" alias (accessible
in menu).
Switching between pages is possible with use ALT + mouse wheel or
"[", "]" keys.

The commit adds also MATCH category to favourites, shows category name
in settings of favourites and cleans up some tabs.
Add custom description of demos

Custom description is displayed in "Watching demo" and "Play demo" menu.
Improve vote info

The commit:
1. adds additional small vote result for hidevote < 2, visible below radar,
2. sets default value of hidevote to 1,
3. shows final vote result in console
4. binds to H key toggling between hidevote 1/2 and 0.