Removed redundant fields DIMENSION::m_arrowD1O, m_arrowD2O, m_arrowG1O, m_arrowG2O (==m_crossBarO/F).
Added DIMENSION::SetOrigin(), DIMENSION::SetEnd(), DIMENSION::GetOrigin(), DIMENSION::GetEnd(), DIMENSION::GetHeight().
Fixed flipping for DIMENSION class.
Added an information that helps to understand roles of the points in the DIMENSION class.
Some minor changes to PCB_PAINTER (mainly using const COLOR4D& for taking the result of GetColor() function).

Drawing tool reacts to rotate & flip events while placing a text.

Removed an unnecessary header from class_board_item.h.

Added KiCad-style modification methods (hover over an item and press a hot key, without selecting first).
Modification point is selected basing on the number of selected items.
Rotation angle setting (Preferences->General) is taken into account while rotating.

- pcbnew.InteractiveSelection.Single for selecting a single item
- pcbnew.InteractiveSelection.Clear for clearing the selection
Made SELECTION_TOOL::clearSelection private.

SELECTION_TOOL::SELECTION::Clear made private, as there was no chance to call it outside the SELECTION_TOOL class.