New config settings an related GUI features

This is a collection of features that would make the experience nice in the app's concept in search entries in general.

• Allow passing the text editable components of the search filter components in the left panel to the central panel when clicking the "+" button to add them to the central widgets.
• The search results table does not support units at the moment.
• An option to limit the number of significant digits in config.py displayed for a quantity would be good. (See the attached screenshot as an example)
• Pre-defined a search filter for looking only at a pre-filtered set of entries. i.e. results.material.functional_type=solar cell for looking at only Solar Cells in the solar cell app.
• Columns from text quantities of type arrays get displayed by joining the items of the array without any separator.