Proofread strings.xml for American English.

Updated main/res/values/strings.xml to fix minor errors in English spelling and grammar.

Fixed a missing backslash.

Silly me.

Minor changes in strings.xml wording

Integrated suggestions by other c:geo developers.

refactoring: cleanup

fix #2994: have [NUMBER] template respect cache source

Prepare addition of OKAPI for oc.pl

refactoring: extract constant

Fixes #2931 - make Handler static to solve lint

fixes #2999: no prefix merged for merged strings