Fixes #28 #29 encoding and env variables in subprocess call

This commits fixes encoding issue using getWindowsCodePage
from Grass7Utils.py

All method in OtbUtils are decorated as static and is now in OtbUtils
class.

Instead of writing a cli_file at startup, provider now pass all
required env_variables in subprocess.popen.

Logging of output from otbalgorithm and updating progress bar is
slightly updated to work with all otb versions.
Algoirthm is launched directly using otbApplicationLauncherCommandLine
`encoding` (on windows) and env arguments passed to subprocess is
logged in QgsMessageLog