Enhancement: improve calendar filter layout

[mikeyarce]

Currently if you go to Dashboard > Calendar here's what the filtering looks like:

We should improve the styles to be more consistent.

A few things that stand out:

• There are multiple types of down arrows used
• The alignment is off
• On smaller screens it's worse
• Some boxes have labels, others do not
• Dropdowns have different UI's! The Category one is a custom UI, the number of weeks is the system default
• It's not easily evident you can "type to search" in the User or Category dropdowns