move partition offset to parameters

Conflicts:
	lib/src/main/java/net/alphadev/usbstorage/partition/MasterBootRecord.java
pass on partition offset in bytes instead of logical blocks.

fixes issue #41.
calculate absolute offset (in blocks) from given bytes.

also previously the offset was the same for subsequent calls. this resulted in the bulk block device to always return the same blocks.
finally fixes issue #24.
Merge branch 'feature/issue-41-partition-offset-fix' into dev