Restore lesser British hills from OpenStreetMap by merging and pruning duplicates.

 * Prepare merged BIH + OSM database using distance between peaks to determine whether to delete the OSM peak or not.
 * Include instructions on how to carry out this merge using Oracle (I wouldn't know how to do the same in MySQL so someone experienced in that might want to have a go and document the steps).
 * Add a few log entries for when DB copy takes place.
 * Increment DB version from 8 to 9 and vacuum to minimize DB file size.
Label rendering tweaks to improve readability and number of distant hills.

 * Fix labels disappearing when only height display is enabled.
 * Extract methods from onDraw() to clarify sub-tasks.
 * Introduce constants to ease testing and pave the way for a configurable minimum text size.
 * Increase minimum alpha and font size to make distant hills just about readable.
 * Continue populating hills even if we've reached the minimum font size; allows more hills to be displayed.