Add possibility to restore Bitmap from a file.

[opankiv]

Read Bitmap from a file and load it to FreeDrawView.

[RiccardoMoro]

For now it supports state save and restore only with the following methods
FreeDrawSerializableState getCurrentViewStateAsSerializable()
and
restoreStateFromSerializable(FreeDrawSerializableState state)

[opankiv]

Yes. But it will be useful to have an ability to read Bitmap data from an external file (maybe previously saved locally) and load it to FreeDrawView for further editing.

[wlmirand]

Agreed. Used the Library to save a signature into a Bitmap file, but needed to load it from the file.