Fixed bug with getValue() failing when in sourceview

[leonardteo]

This fixes the bug where editor.getValue() fails when the editor is in source view (contenteditable mode).

[pulges]

It fixes the outcome of the error , but not the error itself.

From my point of view the toolbar component directly assigning editor.currentView object to string ("source") is not expected or valid thing to do for starters.

It would be better if editor.currentView should actually be pointed to the wysihtml5.views.Textarea as the view in return should have a getValue method (textarea has). (like it is done here: https://github.com/Voog/wysihtml/blob/master/src/editor.js#L111) Otherwise opening the html view allows bypassing the parser rules (user can save not allowed html to server and upon reloading editor later it starts clearing code unexpectedly too)

It requires rebuilding the toolbar component though