Fix third-factor plasticity buffering and add Bouhadjar network tutorial

[clinssen]

Should be merged after #879.

Todo

• [x] Extend and fix issue with third factor plasticity test: it should also be using a buffer for postsynaptic values, alike to the Clopath neuron's buffer for postsynaptic V_m (and derived) values
• [x] Add coco to check that when specifying ports and variable names as post_ports code generation option, these variable names and port names exist; give a friendly error message. -- Spun off to #1009.
• [x] Fix issue with resolution()/get_parent() being very slow -- Spun off to #1024
• [ ] Clean up

[clinssen]

Superseded by #1027 and #1026.