New feature: bitmap smudge

Finger smudge can move colors, smooth them and create colouring effects.
Depending on the length and pressure of strokes, the resulting effect
changes a bit.
Merge pull request #188 from eVoLuTiVeMEDIA/master

New feature: bitmap smudge
Smudge enhancement: second version (may require a final polish)

1.Now, smudge displaces pixels. (in bitmap layer)
2. Slow drag produces produces small  displacement while quick drag
produces larger displacement.
3. Smoother results by setting feather to maximum value.

Remark: The added function drawTexturedBrush (similar to drawBrush) can
be used to easily create a "cloner tool" or to add static textures to
the "brush".
Merge pull request #189 from eVoLuTiVeMEDIA/master

Smudge enhancement.
Merge branch 'master' into feature/object-save-loader
Merge branch 'feature/object-save-loader' of https://github.com/chchwy/pencil2d into feature/object-save-loader