Fix inconvenient default shortcuts in the Mesh Transform tool

The patch bascially makes symmetric transforms be the default choice
available without any modifiers.

Now the shortcuts are the following:

1) Mesh node:
   - click+drag --- move node

2) Border node:
   - click+drag --- move node
   - shift+click+drag --- move whole row/column
   - ctrl+alt+click+drag --- split/slide row/column
   - ctrl+alt+click+drag-away --- remove split

3) Control point:
   - click+drag --- change control point symmetrically
   - shift+click+drag --- change control point non-symmetrically;
                          this action will create angular texture
                          artifacts
4) Node or Control:
   - ctrl+click --- select multiple nodes

5) Patch area:
   - click+drag --- free patch deform
   - shift+click+drag --- move whole mesh

6) Empty area outside mesh:
   - click+drag --- rotate mesh or selection
   - ctrl+click+drag --- scale mesh or selection
   - shift+click+drag --- move mesh or selection

CC:kimageshop@kde.org