Improved search UI and config

Part of #1113 (closed) that fixes the following:

• 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.