settings: integrate new settings system into CSettings
settings: replace CSettings and CGUISettings with new CSettings
added actions settingsreset and settingslevelchange
add SettingLevel to CViewStateSettings
CGUISpinControl: support (string, string) entries
settings: integrate new settings system into GUI
[win32] update VS project files
[confluence] add sidebar to settings view
WIP: guilib: add invalid input state to CGUIButtonControl

This adds HasInvalidInput(), SetInvalidInput(), GUI_MSG_INPUT_VALID and
GUI_MSG_INPUT_INVALID to CGUIButtonControl et. al. Furthermore the following
tags have been added for skins: <textureinvalid>, <alttextureinvalid> and
<invalidcolor>.
add <textureinvalid> in SettingsCategory.xml