Too slow loading of activity diary

[vincentvanhees]

The loading of large activity diary files by g.conv.actlog.R is too slow when processing diary files with > 10000 rows.
I am currently preparing a fix.

Additionally, make sure that diary loading is skipped when activityDiary.RData (or sleeplog.RData in the case of sleeplog) file exists and is not older than activity diary csv file.