Add button for manual timer value

[sswart]

Adds an input and button to manually set the timer value.

I like to use 'uncommon' values like 7 minutes or so. With this change, instead of having to manually put it in the url, we can use the new input/button combination.

Few side notes:

• It's not perfect, no real validation besides the input type
• For numbers higher than 60, it uses the modulo 60 as its value (eg putting in 70 results in a 10 minute timer)

[rajbos]

Looks good, thanks!