GPII-593: All On/Off toggles can be switched with the Enter key

Link to JIRA: http://issues.gpii.net/browse/GPII-593.
Also made the Speak Text and Braille On/Off adjusters use the reusable "gpii.adjuster.onOffSwitch" grade instead of custom ones.
Some styling inconsistencies introduced should be resolved within https://github.com/GPII/prefsEditors/pull/15; that is basically the width of the adjusters compared to the ones in Change Contrast and Increase Size.
Also, a problem with input IDs and related labels' "for" attributes has came up, which was overcome by using a duplicate template with different ID for an input. Note that this duplicate template was already needed because of the slightly differentiated UI of the Braille adjuster.