Subcategories shouldn't belong to a single category

[dougy83]

All components with the same subcategory name should be filtered together; currently they are filtered based on their category and subcategory combined.

For example, if I want to filter "Light Emitting Diodes (LED)" (subcategory name), I have the following categories + subcategories available to select:

Category	Subcategory	Number of components
Embedded Processors & Controllers	Light Emitting Diodes (LED)	1
Optocoupler/LED/Digital Tube/Photoelectric Device	Light Emitting Diodes (LED)	1128
Optocouplers & LEDs & Infrared	Light Emitting Diodes (LED)	37
optoelectronics	Light Emitting Diodes (LED)	2
Optoelectronics	Light Emitting Diodes (LED)	2186

These are all LEDs, and should all be filtered, irrespective of the category selected. E.g. if I selected the option in "Optocoupler/LED/Digital Tube/Photoelectric Device", I would only see 1128 components, and not realise that there's another >2000 LEDs that I missed.

Correcting this is probably a fair bit of work; a simpler fix is to add a checkbox at the top of the categories section called "Include all matching subcategories", which allows (de)selecting all select items with the same subcategory name by (de)selecting that subcategory in a single category multiselect.

As an aside, the category names should be grouped ignoring upper/lowercase; this can be done when the server processes the database.