Implement smtkTruchasPlugin, initially for custom views
  Add smtkTruchasCoilsView::isEmpty() method
  Fix issues with source model sorting
  Fix logic for drag/drop coil position in both tables
  Bug fixes, mostly related to display
  Finish class renaming
  Rename custom view to smtkTruchasCoilsView per smtk convention
  Hide the unused up/down buttons
  Build smtkTruchasPlugin
  Move qtInductionCoilsView to plugin directory

* Fixes source model missing emit dataChanged (2 places)
* Changes logic to disable sorting if any times are unset

BOTH coil and source models must be updated together, since
both models are affected when the attribute is modified.

* Wasn't returning "editable" data, i.e., QVariant(QString)
* Wasn't dealing with set/unset state
* Wasn't handling all background conditions
* Wasn't handling all "n/a" conditions

Based on comment in RGG that: modules that aren't loaded as direct
dependencies of CMB modules will not be found.

Custom view induction coils

See merge request cmb/plugins/truchas-extensions!2

* Enables drag when single/complete row is selected.
* Adds qtDragSelfFilter to prevent dragging from one QTableView into
  the other.

* Update both models to emit dataChanged signals
* Add logic to check montonically-increasing order

* After adding row (coil or time step), select first column of new row
* If coil selected in coils table, select corresponding column in
  source table

* Add default values to sbt
* Display "n/a" for first time value
* Display invalid background color for unset time value
* Handle case when induction-heating attribute missing
* Also fix some clang formatting

Also
* Migrates addCoil() and addTime() methods to Internals
* Adds up/down buttons to layout (not implemented)
* Adds message box for features not yet implemented

Connect buttons for add coil and add time (row)