Add new tools.py to handle subcommands.
Most workflow moved to subcommands handlers, which in turn calls
tools.py functions.
Moves internal state (dict which gets parsed into PFState) to folder
.pfstate (sort of like git) and renamed to state.
New PFState class and factory pfstate function added.
*.pickle changed to .pfstate on .gitignore. Everything local stored in
.pfstate.
Adds vacation, status and backup commands. Modifies init, restart and
parse to receive PFState and call tools functions.
Vacation can add, list or remove vacations date intervals.
Backup saves either a full transaction list or the entire data folder
into .pfstate/backup folder.
Categorization functions moves to tools, deleted old one on
categories.py.
Moves parse_data and load_transactions/save_trasactions outside of
respective class to global scope.
Travel category class moved to the end of file, since it uses others in
its search method.
Removes unused initializer.py file.
