Impove performance when retrieving time series for set of epochs

[ehennestad]

For the NDI-Marder project, profiling the element method plotEpochs uncovered some performance issue.

Profiling was done on session '412691d3730ea2a0_40cb949cfbed9eba', element: ntrode/dgn-1

Total time before making changes: 21.1 seconds

1. Repeated calls to ndi.file.navigator/getepochfiles_number
   Todo:

   • Cache the result in a map where epoch number is the key and the resulting file path(s) is the value.

2. Repeated calls the the database to check for ingested documents with the same query parameters.
   

   NDI-matlab/+ndi/+file/navigator.m

   Lines 477 to 480 in 5705f29

   	epoch_query = ndi.query('','isa','epochfiles_ingested') & ...
   	ndi.query('','depends_on','filenavigator_id',ndi_filenavigator_obj.id()) & ...
   	ndi.query('base.session_id','exact_string',ndi_filenavigator_obj.session.id());
   	d_ingested = ndi_filenavigator_obj.session.database_search(epoch_query);

   
   This is called once per each epoch (107), resulting in total call time of ~3 seconds to mksqlite.
   @stevevanhooser What about caching the result in a temporary cache with a timeout of e.g 1 minute? Other ideas?

3. Repeated calls to abfloaf
   There are 107 epochs, but 555 calls to read abc_header, totalling ~2 seconds.
   Todo:

   • Can this be improved?

[ehennestad]

Total time after doing 1: 15.5 seconds

[stevevanhooser]

Cool, thanks. Should this be a pull request yet or should we wait?

[ehennestad]

Still want to work on points 2 & 3

[ehennestad]

Total time after doing 2 & 3: 11.1 seconds