ENHANCEMENT: Add instrument resolutions of specific instruments

Another thing that was brought to me during NMSUM. Currently, the only way to input an instrument resolution to MDANSE analyses is by manually typing in the parameters of the Gaussian. This is often not trivial, especially for external users who do not have this information at hand, and so might have to contact an instrument scientist or do extensive searches. Overall, this wastes everyone's time and makes for a bad user experience.

Therefore, a drop-down box should be implemented that allows users to select a specific instrument, the resolution of which would be automatically filled in, similar to how it is in Mantid.