Converted plot_mesh_tally.py to use Tkinter rather than PyQt.
Converted plot_mesh_tally.py to use Tkinter rather than PyQt.

johnnyliu27/openmc,shenqicang/openmc,liangjg/openmc,paulromano/openmc,lilulu/openmc,shikhar413/openmc,walshjon/openmc,smharper/openmc,mjlong/openmc,mit-crpg/openmc,kellyrowland/openmc,mit-crpg/openmc,samuelshaner/openmc,bhermanmit/openmc,walshjon/openmc,amandalund/openmc,sxds/opemmc,samuelshaner/openmc,lilulu/openmc,bhermanmit/openmc,nhorelik/openmc,shenqicang/openmc,amandalund/openmc,wbinventor/openmc,walshjon/openmc,johnnyliu27/openmc,walshjon/openmc,smharper/openmc,samuelshaner/openmc,smharper/openmc,mit-crpg/openmc,sxds/opemmc,paulromano/openmc,johnnyliu27/openmc,amandalund/openmc,liangjg/openmc,wbinventor/openmc,paulromano/openmc,shikhar413/openmc,smharper/openmc,johnnyliu27/openmc,mjlong/openmc,amandalund/openmc,kellyrowland/openmc,mit-crpg/openmc,wbinventor/openmc,nhorelik/openmc,liangjg/openmc,paulromano/openmc,lilulu/openmc,samuelshaner/openmc,wbinventor/openmc,shikhar413/openmc,liangjg/openmc,shikhar413/openmc