Marginally reduce event rate to be manageable.

Jira issue: WP-112
Fix removeEventListener methods.

Jira issue: WP-112
Add testbed support for device motion events.

Jira issue: WP-112
Multiple minor fixes

Jira issue: WP-260
Allow getCurrentPosition() to be synchronous or asynchronous
according to implementation and availabiity of position.

Jira issue: WP-260