Change input widths of Generic task forms

[mockoocy]

Currently forms for generic tasks are displayed in modal, which takes 50% of the whole window width.
The containers containing form inputs are rendered using Bootstrap grid system - they have classes col-x, where x is between 1 and 12 or auto.
The inputs take the whole width of the container, which corresponds to 25% of the whole window width.
They seem far too big, as they are meant to contain only few characters.

Relevant discussion: #1678 (comment)