WebUI: make multi-value dialog more compact

[inaky-intc]

Current representation of the multi-value dialog for the inventory was taking a lot of vertical space, when we have plenty of horizontal available.

This is the dialog that pops when a cell in the inventory has too much data (because it is an aggregation of multiple values).

Reformatted to be a simple table with the keys and values side by side; header in a single line with a close button represented by an X.

New looks like:

Old looked like: