Registered Only Server

Implemented the ability to set the server to only allow registered
users.  Also updated client to reflect the log-in rejection as well as
put a check in place for the server to not start if db connection is not
available yet registration is required.
Requested Cleanup

Corrected tab to 4 space (per request)
Moved regonly option under authentication ini location (per request)
Stale Comment Removal

Removed stale commented lines from about window code.
Merge remote-tracking branch 'upstream/master' into registered-user-only-server

Conflicts:
	common/server.cpp
	common/server_protocolhandler.cpp
	servatrice/src/servatrice.cpp
Merge remote-tracking branch 'upstream/master' into registered-user-only-server
Before: If default is checked, Oracle will always save to the AppData path.
If a path to cards.xml is set, Oracle will update that cards.xml.
If Oracle is run before a path to cards.xml is set, if default is checked, cards.xml will be saved on the AppData path. Furthermore, this path will be set as the cards.xml path for both Oracle and Cockatrice.
If Oracle is run before a path to cards.xml is set, if default is NOT checked, cards.xml will be saved at the selected path and this path will be set as the cards.xml path for both Oracle and Cockatrice.
If a path to cards.xml is set, if default is NOT checked, cards.xml will be saved at the selected path but this path will NOT be set as the cards.xml path for either Oracle or Cockatrice. This allows people who already have a cards.xml (which may be customized), to still obtain clean copies of cards.xml through Oracle without overwriting their own
Removed some redundant code. Factored out translations.
Added a button and the functionality to clear all downloaded images (all images within subfolders at picsPath/downloadedPics) under Settings.
Logically inverted the if... else statement by removing the logical not (!). Cleaned up a ;;.
Added notification messages informing users of the success or failure of clearing downloaded images.
Moved the button from the paths section to be below the "Download high-quality card pictures" checkbox. Button now reads "Reset/Clear Downloaded Pictures". Removed "Path to"s from card/token database, hand/stack/table/player info background, and card back labels.
Added section on memory management to CONTRIBUTING.md.
Merge pull request #269 from arxanas/style-guide-memory-management

Added section on memory management to CONTRIBUTING.md.
Fix crashes trying to load the picture of a card with no <set>
Don't save card pictures if we don't have a proper set name for it
Fix off by one
Merge pull request #271 from ctrlaltca/picurl_handling

Picurl handling
Merged: First draft of better pic url error handling

Cherry-picked b9cb61abd05f83c67740aafa5e1e6939143547e4
Continue downloading card images after failing url on one.

I should probably bust this out to a method.
Don't leak a QSettings object at every logged message