integrate simpleCart with parent libmon-php installation

[bibliocoll]

in case JT is part of a libmon-php installation, make sure that

1. simpleCart data is passed back and forth in a consistent and useful manner
2. checkout actions can handle cart entries provided by libmon-php
3. deal with all the cringy corner cases i haven't thought of yet

[krugar]

this is part of milestone 0.1, but since it needs to be done after the release of 0.1, do not track it via the milestone

create a second release branch for the libmon-integrated version with:

• simpleCart integration/handoff
• the "back button"

then

• add simpleCart + handoff to libmon-php
• submodule the then new JournalTouch-libmon release branch in libmon-php

...

• profit? 😉

[krugar]

i want to get away from moving data around unneccesarily (and unchecked) between server and client. that breaks the current "simple" plan of using simpleCart as a vehicle for libmon-php data, but imho that is the lesser evil 😛

this means libmon-php will have to evolve towards a common data standard and session support, as tracked in bibliocoll/libmon-php#1 now.

on this side of the project boundary, i'd like to have the dual-release thing ready for 0.4 (what was mislabeled as 0.2 before), but that will require at least two things:

• the cart/session data format to be general enough to work libmon-php data
• the cart/checkout part of JournalTouch being contained in a module that can be ported into libmon-php.