fix Sessions OOP handling
add json.lua module for json handling
loading the json module wasnt working as expected
added default session functions as placeholders for a compatibility layer
Let Session handle getting the current session

- rename sload to parse
- added Session:copy_curr()
- get() now uses copy_curr()
code cleanup
make Session's and related tables clone()'able
renamed save() to store()
adjusted sload() to use my Session interface
adjusted open() to use my Session interface
adjusted store() to use my Session interface
added first version of add() for the JS API
code cleanup
move copy_curr() from Session to session
moved out Session Datastructure to its own file for easyier testing.

- corrected Session:parse() a bit, still not complete though
- TODO: fix Session:parse() so that it really restores the whole OOP methods (atm only Session and Window are restored)
Added listing existing Sessions to the get() JS method
fix the new() methods in SessData

- dont use __index but rather set the attribs in the new() method
fix clone() and __tostring()

- clone() wasnt returning anything
- added a hist representation to __tostring
reminders to look into ipairs usage
added from_table()

- Ability to create a new Session object from a table. Needed to turn the json encoded data back into objects.