Improve load game UI

[historic_bruno]

Currently when loading a saved game, it shows a list with timestamp and map name for each game. I would like to see at minimum:

• Timestamp
• Map name
• User's description of the game
• Players
  • Name / player number
  • Civ
  • Status (defeated/active)
• Elapsed time

Possible enhancements:

• Small screenshot
• Game version; mod(s) used

It doesn't all have to be shown on one line, but rather have a common UI panel to display details for the currently selected game.

[Philip Taylor]

Also it should be possible to delete saved games from the UI, since people apparently like keeping their list clean.

[ben]

In 11233:

Adds saved game deletion. Refs #1090
Documents a few things related to saved games.

[historic_bruno]

#1683 was a duplicate.