Rework loading and unification

Rework the loading of SVD data and unification into single shared SVD space to conform to new structure of datasets. This includes:

[x] Implement session and set aliasing in config loading
[x] Seperate entry and unification into distinct rules
[x] Add and fill datasets column
[x] Implement trial selection to get sessions/sets from unified dataset in shared space
[x] Implement accumulation strategies
[x] Test everything

michaelschaub / calcium-imaging-analysis