build expression creation function

[jdeepee]

Expression functions requires the following functions:

• Creating of expression from given expression times and insertion into holochain w/ validation
• Creating of any channels which do not exist but which are specified in post
• Linking of created channels to relevant Den/Group locations
• Linking trees for searching created between channel(s) and any other items which are present in the contextual links list
• Remember all contextual links must completely link together with searchable link paths