primality: Update brute-force primality algorithm to perform fewer operations.
primality: Use the most vanilla themes as possible.
primality: Try a more minimal layout, with fewer components.
primality: Remove elipsis from button.
primality: Remove unused strings.
primality: Fine tune layout with padding on the output by 10dp.
primality: Remove ellipsis from the right string.
primality: Make description match parent, instead of content.
primality: Set margins to the recommended 8dp (only on the left).
primality: Make height of input equal to that of the button.
primality: Remove explicit centering.
primality: Align output with the button.
primality: Put scroll view relative to the input.
primality: Put the answer in the input field.
primality: Remove unused import.
primality: Remove unused TextView.

This, by the way, makes us friendlier to devices with small screens, which
is just an added benefit, also uncluttering the interface.
primality: Set minEms of input field to 10.
primality: Change the name of the app to be more descriptive.