ENH: pva image dim order option

[nstelter-slac]

add option for specifying how pydm should read pva image dimensions.

more context: https://github.com/slaclab/pydm/issues/1082

[nstelter-slac]

This should keep current behavior when reading existing working pva images, but now also give the option to fix broken ones that have different dimension ordering in their sent-data.

To see how this patch fixes the address 'LAS:LHN:BAY3:CAM:NF2:IMAGE2:Pva:Image':

ssh -Yt <linux-username>@centos7.slac.stanford.edu
ssh -Yt psbuild-rhel7
source /cds/group/pcds/setup/epicsenv-cur.sh
source /cds/group/pcds/pyps/conda/pcds_conda
//clone pydm or have existing local pydm repo
//checkout this patch
cp ~tjohnson/junk/bay3_pva_test.ui ~/
cd pydm/pydm_launcher
PYTHONPATH=../ python main.py ~/bay3_pva_test.ui
open in designer
click on image view and go to properties
change new option 'dimensionOrder ' to 'widthFirst'

with dimensionOrder as widthFirst, you should get something similar to this: