Add "max" and % slider options in amount inputs

[0xSachinK]

Add max button in the Opin input field. Also we can add something to indicate the fact that OPIN tokens would be burnt upon pinning a given issue. Maybe a "Burn" label to left side of text field. Or a placeholder text "Burn OPINS" in the input field.

[mktcode]

A note on the burning is definitely reasonable. I'm not sure about the max button though. While it's kind of a standard now in every wallet you see (and should of course be implemented in the send/deposit forms), I'm not sure if it makes a lot of sense in that case. Why would you want to burn all your tokens if you technically just need 0.0000000...1 more than the first issue on the pinboard? On the other hand, if it does not clutter the UI too much.... why not.