GUI bugfixes and improvements for beta release

Several GUI bugfixes and improvements, including:

• Added search filter for xc_functional_names, enabled ES suggestion for xc_functional_names.
• Fixed issue with aggregations requests using a wrong default size of 5 items when dealing with a fixed, enumerated set of options.
• Removed statistics from author_name
• Increased default statistics size of datasets.dataset_name to 10
• Correct use of plural and singular form of results/result in the GUI through a generic utility function that can be also used to pluralize other values.
• When pressing "show more" and not finding any new values, the "show more" button now is disabled and has a tooltip indicating that no more values are available.
• Empty containers assigned as filters are now handled as if now value was assigned at all.
• Sections are no longer suggested in the search bar and trying to set a value for a section from the search shows an appropriate error message.
• Suggestions list is now cleared whenever the input field is cleared.
• The periodic table statistics are now correctly updated when the periodic table is "anchored" in the statistics grid.