added mandatory client log file

- a client will now write all os console messages to "clientlog.txt"
- at every game start, the log file gets rotated (with five old logs kept)
- commandline parameter "-N" can be used to limit the number of lines
  (after the lines are logged, the file is closed)
Fix switching from spectator to active team in bot modes

Before this fix player could switch from spectate to alive mode,
but he stayed in SPECTATOR team.
Note: 2 mouse clicks are necessary to player's spawn. Second respawnself()
is needed, because spawnplayer() is executed before server will switch
player1 to active team, so he would always spawn in CLA base (in bot
team modes).
Show always all servers after forcing serverlist update
Improve "favourite servers" feature

The commit:
1. does serverdescription keyword case insensitive for
showonlyfavourites > 0;
2. fixes typo in argument of alias in keyword;
3. fixes disabling background color for servers of the category, when
alpha is changed to 0;
4. shows 0 instead of 10 in info about digit, which toggles 10th category;
5. adds info about "image" attribute in favourites.cfg;
6. adds new feature: "Search for servers".
Fix warning messages to spammer changing name/skin

Warning message will be sent only to spammer changing name/skin,
and only in multiplayer, what fixes issue:
https://github.com/assaultcube/AC/issues/66
Display HUD messages over some less important info
Keep selected player in op menus, when other player (dis)connects

Until now, when in, for example, kick player menu there was selected
some player and (dis)connected other player with lower CN, then this
earlier selected player was moved to other item in menu, but number
of selected item didn't change, so other player was selected.
Test work - ignore player menu
Add custom description of demos

Custom description is displayed in "Watching demo" and "Play demo" menu.
Add AssaultCube's CodeBlocks project for Linux
Don't show HUD reflection on water surface

For reflectclip > 1 player's HUD reflects on water surface.
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.
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().