Avoid disabling electric-indent-mode globally

Currently, when a feature file is opened, feature-mode gets rid of
electric-indent-mode behaviour by disabling it. However, as it is a
global mior mode, this has the effect to disable it globally.

This commit removes the deactivation, and instead configure it so that
it does not indent anything.
Merge pull request #61 from stevenremot/avoid-disable-electric-indent-mode

Avoid disabling electric-indent-mode globally