add margins around images in PageRenderer
* add test scripts borrowed from I2P
  - checkxml requires tidy for HTML files and xmllint for XML. Tidy is used
    because it will exit non-zero on parsing errors while xmllint will still
    exit 0 if the HTML files contain errors. xmllint "does the right thing" for XML.
  - checkpo requires msgfmt
* add testscripts build target
html fixes
Russian translation from Transifex
- Tag PageRenderer menu for translation
- Hide most of PageRenderer menu when used in post preview or PageRendererTab/HelpTab
- Cleanups of listener classes in PageRenderer
merge of '03bfae634968a475d5a4f8c46e380cdc8657b4d9'
     and '5a24ff21c9fe4b110d31d20b17e2c3fa108f0905'
- Tag more strings
- Refresh English po file, 88 new strings