Update po/en-US.po

The modified string seems not to be complete or bad translated. My proposal is what I understand it means. This string also appears on other files, but I'm only changing it here as a proposal.
Update help_data/en/index.wiki

Some strings seemed hard to understand, this is my proposal as I understood them. Also, as I haven't found "Watch Window" strings in the files, so "Watching Window" seemed to me more appropriate.
Merge pull request #2 from strel/master

Fix English strings changes proposed by strel