Add extractImageNFI for extracting dreambox NFI images

extractImageNFI is based on gutemine's nfiextract.py
OMBManager: check if getImageFileSystem contains jffs2

Required for dreamboxes because filesystem is jffs2.nfi

>>> getImageFileSystem()
'jffs2.nfi'
OMBManagerInstall: check if getImageFileSystem contains jffs2/ubi

Required for dreamboxes because filesystem is jffs2.nfi

>>> getImageFileSystem()
'jffs2.nfi'
OMBManagerInstall: fix extractImageNFI function add missing self
OMBManagerInstall: add missing struct import
OMBManagerInstall: correct variable p to part
OMBManagerInstall: enable padding for kernel
OMBManagerInstall: make block2mtd erase size configurable
Revert "OMBManagerInstall: enable padding for kernel"

This reverts commit 7ab293b8365d2ec1f8a89661bca4ab481b9c99ae.
OMBManagerInstall: extract kernel.bin unmodified
OMBManagerInstall: add jffs2 extension to dreambox kernel
OMBManagerInstall: add missing parenthesis
Add unjffs2 utility for jffs2 filesystems

When unjffs2 utility exists don't search for kernel module
OMBMAnagerInstall: unjffs2 the rootfs not the mtd
OMBManagerInstall: don't use jffs2 extension for dreambox

OpenMultiboot should handle dreambox nandwrite/nanddump parameters
when OMB_DREAMBOX is defined at compile time
OMBManagerInstall: remove padding from nfi images
OMBManagerIntall: make VID header offset configurable
OMBManagerInstall: make nandsim parameter configurable

Because some Dreambox models require differect nandsim parameters
in order to properly recognize ubi.
OMBManagerInstall: remove not in use variable flashsize
Merge pull request #3 from athoik/dreambox

OpenMultiboot: Initial support for Dreambox