Proof of concept for tabwidget template

TabContainer, headlines automated, dynamic attribute access

TODOs: RenameLabel support, icons below minimap (left/right area)

Conflicts:
	content/gui/xml/ingame/tabwidget/ships/overview_war_ship.xml
	horizons/engine/pychan_util.py
	horizons/gui/tabs/tabwidget.py
Add settlement.name and tier.inhabitant_name properties

settlement.name is a shortcut to its NamedComponent, intended for use
with the new TabWidget, but probably not limited to that.

inhabitant_name is a property of tier overview tabs at the main square.
tabwidget: Rewrite and relayout mainsquare_inhabitants
tabwidget: Rewrite and relayout overview_{signalfire,tower}

Two proof-of-concept tab conversions.
tabwidget: Rewrite and relayout editor_settings

Conflicts:
	content/gui/xml/editor/editor_settings.xml
tabwidget: Rewrite and relayout overview_tradership
tabwidget: Rewrite and relayout overview_enemy{building,unit,warehouse}

Entirely removes the currently redundant overview for enemy units.
To be added at a later point where such units' information displayed in
those tabs is actually different from enemy buildings.

Conflicts:
	content/gui/xml/ingame/tabwidget/overview/overview_enemywarehouse.xml
	horizons/gui/tabs/shiptabs.py
tabwidget: Rewrite and relayout overview_{firestation,resourcedeposit}
tabwidget: Rewrite and relayout overview_settler

Conflicts:
	content/gui/xml/ingame/tabwidget/overview/overview_settler.xml
tabwidget: Rewrite and relayout overview_productionbuilding
tabwidget: Rewrite and relayout boatbuilder
tabwidget: Rewrite and relayout diplomacy

Conflicts:
	content/gui/xml/ingame/tabwidget/diplomacy/diplomacy.xml
tabwidget: Rewrite and relayout island_inventory

This needs more love for the dynamic background icon generation still.
tabwidget: Rewrite and relayout overview_select_multi
tabwidget: Rewrite and relayout overview_{trade,war}_ship

Conflicts:
	content/gui/xml/ingame/tabwidget/ships/overview_trade_ship.xml
tabwidget: More inheritance for ship overview tabs

Because we're cool like that.
Note that the plain ShipOverview tab does *not* specify a widget xml, so
it cannot be used as stand-alone tab!

Conflicts:
	horizons/gui/tabs/shiptabs.py
tabwidget: Rewrite and relayout tradetab
tabwidget: Rewrite and relayout buysellmenu
tabwidget: Rewrite and relayout tab_account

Conflicts:
	content/gui/xml/ingame/tabwidget/warehouse/tab_account.xml
	horizons/gui/tabs/buildingtabs.py
	horizons/gui/tabs/mainsquaretabs.py
tabwidget: Rewrite and relayout buildtabs