fleet duration input hh:mm

[Isoterik]

make the fleet duration input only available in hh:mm for better statistical processing.

[Isoterik]

forgotten to mention releated commits: https://github.com/codepreller/eve-participation-system/commit/a7b725f40fec3f65f4dfdb01fc8828283b95f331 https://github.com/codepreller/eve-participation-system/commit/084178ead82344edbe6f2aca53ebfeaa8abb6139

[codepreller]

after discussion:

• switching hours and minutes dropdowns to start and end datetime field tag
• adding started_at and ended_at to the db