[#74392582] Allow searching by model

This is a cheap speed improvement which might
be useful in the short term, especially when
someone isn't searching for assets.

However the asset search is fundamentally slow
via MySQl so this is not a long term solution.
Merge pull request #885 from JamesGlover/74392582_ss18_-_speed_up_search_(top_right_sequencescape)

[#74392582] Allow searching by model