Add folding panel

also add missing EncodingPanel
Improve python code folding

Display real scopes and not just indented blocks.
QIdle: fix for python2 (the zip path were not transmitted to the server)
Fix for None previous block
Fix auto complete on first line (previous cursor is None)
Add support for docstring folding and improve imports folding
Refactoring and cleanup
Fix bug with end of line comments which prevent detection of new fold level
layout() may return None
Merged 'develop'.
Cancel blank lines warning

the folding panel introduces whitespaces so that the fold scope can be properly rendered and remove them when highlight finished, this means the document will be automatically cleaned up and this warning is a false positivie
Fix comment
Rm unused __init__.py
Enable blank lines warning since the hack that consisted to temporarily insert whitespaces has been removed
Merged 'develop'.
Merged 'develop'.
Use pyqode.core @ feature/code-folding for testing this branch
Merged 'develop'.
Merged 'develop'.
Fix tests (infinite loop when detecting docstring fold indent)