Add better search and filtering functionality to flights index

[calumshep]

Current problem: there are at least 3 different pages displaying tables of flights, creating repeated code and confusing navigation.

Solution: combine all flights which are not marked as complete (i.e. those which are open, accepted and awaiting planning or those with active flight plans) into one single page (but with different tables still).

Drawbacks and alternatives:

• Could cause confusion between what flights are open to being accepted and what have already been accepted, etc. Need to consider pagination for open requests as well.
• Perhaps open flights need their own search-based page and everything else goes on one page?

Notes:

• Dispatch page should still exist to maintain synchronicity between URLs and navigation links (i.e. there is a 'Flights' link for /flights URLs and a 'Dispatch' link for /dispatch URLs.

[hcphoon01]

Could have all flights on one page, /flights, and within that have multiple tabs for each table.

Reference: https://getbootstrap.com/docs/4.0/components/navs/#javascript-behavior

[calumshep]

Simplified the user-flights page (see 65a28a8)
Work still required to improve the flight searching page(s) and maybe add some more links to the sidebar, etc. (just improving overall nav/UX)

[calumshep]

Logbook still to be implemented

[calumshep]

Dispatch link was added to sidebar in 9fee403#diff-564871892805fdcda63f190c78a0eaceR30

[calumshep]

projectFLY-style searching to be added to index page. Also consider implementation of user 'filters' where a user can save a specific search query and subscribe to a feed of notifications when new flights appear for said query