added Activities API

[bigcat88]

Also added nc_iso_time_to_datetime internal method to parse time for shares, notifications and activities.

This leads to fix of a bug when NotificationInfo.time was always incorrectly parsed and equal to datetime(1970,1,1)

[codecov]

Codecov Report

Merging #112 (31b389c) into main (870b6af) will increase coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #112      +/-   ##
==========================================
+ Coverage   99.71%   99.72%   +0.01%     
==========================================
  Files          29       30       +1     
  Lines        2446     2552     +106     
==========================================
+ Hits         2439     2545     +106     
  Misses          7        7              

Files Changed	Coverage Δ
nc_py_api/_exceptions.py	100.00% <100.00%> (ø)
nc_py_api/_misc.py	100.00% <100.00%> (ø)
nc_py_api/_session.py	98.60% <100.00%> (+<0.01%)	⬆️
nc_py_api/_version.py	100.00% <100.00%> (ø)
nc_py_api/activity.py	100.00% <100.00%> (ø)
nc_py_api/files/sharing.py	100.00% <100.00%> (ø)
nc_py_api/nextcloud.py	100.00% <100.00%> (ø)
nc_py_api/notifications.py	100.00% <100.00%> (ø)