Make tide level a numeric input field

Improve the experience on mobile by making the tide levels input box numeric.

Note Android numeric keypads only have a "next" button which is equivalent to
"tab". Therefore we need another form element 1) so that the keypad
disappears and 2) so that "next" doesn't jump up to the location bar.

https://www.pivotaltracker.com/story/show/74506964

[Delivers #74506964]