Steps of escaping process:
1. Executables unescape the string for export(if necessary)
2. Po class work with unescaped string
3. Escape strings to PO format and write out
4. Read from PO and unescape strings
5. Executables make own transformation on string and merge

Use general functions for escaping (helper)
Delete unneeded escaping methods(xrmmerge, merge)
Delete some unused method from PoEntry class

Change-Id: I7f9414581aae9e6de7d1573862a32cdbd68c9545