naming conventions, ogs6py API

Changes default abbreviation from

import ogstools as ot

to

import ogstools as ogs

To get rid of ogs6py import like

from ogstools.ogs6py.ogs import OGS

the class is renamed to Project and is imported in the ogstools init.py, so that we can just do:

import ogstools as ogs

ogs.Project(...)

The arguments are renamed from all uppercase to lowercase.

Fixes #85 (closed)