* Add a way to display flash messages
* Make the flash messages look nice
* Add actual feedback messages
* cargo fmt
* Move flash messages to PlumeRocket
And add trait to convert PlumeRocket to BaseContext
* Remove useless lifetime
* Better contrat for input fields
This change set a white background for input field (text, select and textarea)
to have a better contrast with the page background and improve accessibility for
people with vision problem, and just crappy screen.
This change also remove the round corner for the input to have a clear difference
between editing field and buttons.
This max-width of the form element are a bit bigger too.
* Less space between label and input
