Support for new numeric operators (gt, lt, gte, lte, ne) for table filtering

[kamilfb]

This enhancement is for the system list table filtering, supplementing it with additional operators applicable to numeric fields.

The additional operators are:

• Greater than (gt)
• Less than (lt)
• Greater than or equal (gte)
• Less than or equal (lte)
• Not equal (ne)
• Anything else defaults to equals (the original behaviour)

The format is backwards compatible and works in URLs as before:

• all previous query strings will work as before
• mixed default (equals) and new operator: query:hp_output:5:gt,UFH:0 (output to be greater than 5, UFH quals to 0)

Other examples:

• query:hp_output:5:gt,UFH:0,old_radiators:1,combined_cop:4:lt,combined_cop:3:gt
• query:hp_output:5:gt,UFH:0,old_radiators:1,combined_cop:4:lt,combined_cop:3:gt,combined_flowT_mean:35:lt

You can also specify ranges, e.g.:

• query:combined_flowT_mean:35:lt,combined_flowT_mean:33:gt