incorrect/inconsistent camel case in lang strings

[Dan Marsden]

Moodle convention is to only capitalise the first word.

eg:

$string['activitycompletion'] = 'Activity Completion'; should be:

$string['activitycompletion'] = 'Activity completion';

several other strings that should be updated too.

[David Watson]

Fixes issue #1 (correcting capitalisation in language strings)

→ <<cset 5a69ec41a325>> → <<cset 498395eb7b40>>