Add select and input[type='number'] as choices for time inputs

I added some new inputs/features for a project I'm working on and thought you may be interested in merging them.  

This branch adds several new options to the input:
`:time_input` => `:text` (default), `:select` or `:number`

The following apply to input types: `:select` and `:number`
`:minute_step` => integer 
`:hours_24` => `true` or `false` (default)

Examples:
```
m.input :born_at, 
  as: :just_datetime_picker, time_input: :select, minute_step: 20
# Would render minute select with four options: 00, 15, 30, 45

m.input :born_at, 
  as: :just_datetime_picker, time_input: :number, hours_24: true
# Would render hour as <input type='number'... with 24 options: 00..23
```