Refs #10223 Lower initial Refl UI size
Refs #10223 Decrease whitespace in Refl UI
Refs #10223 Normalise Refl UI button sizing
Refs #10223 Add basic input validation

Instead of processing failing mid-way through due to invalid input,
validate the input first, then start processing.
Refs #10223 Improve const-ness
Refs #10223 Add a progress bar to the Refl UI
Refs #10223 Add new rows after the current selection
Merge branch 'feature/10223_new_refl_ui_improvements' into develop