[FIX] Fix errors from updating dashboard

[DESm1th]

Jer noticed some more errors (Thanks Jer!) from my recent update to the dashboard table organization. This fixes the last of the errors and also rolls out two fixes for older issues

• The addition of the ExpectedScan table means that study.scantypes returns an ExpectedScan object instead of directly returning Scantype, so to get the string tag name line 313 needs to use st.scantype_id. It also means a site name has to be given to get the list of scantypes from a dashboard Study object. af385eb
• This also removes a reference to a variable that was removed from datman.xnat.XNATExperiment ages ago and that was causing periodic exceptions aba55cb
• And makes the dm_deface script executable by default ae79263

[codecov]

Codecov Report

Merging #323 (ae79263) into master (322b28f) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #323   +/-   ##
=======================================
  Coverage   30.87%   30.88%           
=======================================
  Files          62       62           
  Lines        9275     9273    -2     
=======================================
  Hits         2864     2864           
+ Misses       6411     6409    -2     

Impacted Files	Coverage Δ
bin/dm_deface.py	0.00% <ø> (ø)
datman/dashboard.py	27.80% <0.00%> (ø)
datman/xnat.py	27.74% <ø> (+0.06%)	⬆️

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