Numeric fields in 'Add new entry' screen

Currently, both the 'Period (seconds)' and 'Digits' input fields are treated as standard text inputs, which results in the full text keyboard instead of the numeric keypad when editing:

Since these fields are inherently numeric, as checked by parsePeriod() and the digits validation - switching them to a numeric input type would improve UX and prevent input errors.

I suggest annotating the TextInputLayout of both fields to be numeric only. I'm working on a PR for this and will submit it shortly :)