This commit moves the list of transform orientations from scenes to workspaces. Main reasons for this are: * Transform orientations are UI data and should not be stored in the scene. * Introducion of workspaces caused some (expected) glitches with transform orientations. Mainly when removing one. * Improves code. More technically speaking, this commit does: * Move list of custom transform orientations from Scene to WorkSpace struct. * Store active transform orientation index separate from View3D.twmode (twmode can only be set to preprocessor defined values now). * Display custom transform orientation name in header when transforming in it (used to show "global" which isn't really correct).