Reworked the way of processing events in TOOL_MANAGER class.
Added GetCommandStr() for TOOL_EVENT class.

Introduced a new type of action: TA_ACTIVATE to distinguish events activating tools from common tool actions.

Removed TOOL_ACTIONs: selectionSingle, selectionClear. SELECTION_TOOL methods are called directly instead.

bugfix: changing track width/via size using the dropdown menu when custom size was enabled did not change anything.

Reduced number of switched events, allowing to use VIEW_CONTROLS, even if there is no extra event dispatcher.

Event handlers are (dis)connected depending on the active view.
TOOL_DISPATCHER inherits from wxEvtHandler, so now it receives events directly instead of being fed by external handlers.