Docu files looked up in language subdirectory first. Refs: #88.
If a non-standard language is selected in 'Edit->Preferences', the commands StdCmds.OpenBrowser and StdCmds.OpenAuxDialog look up a Docu file first in the language subdirectory. If it is not found, the standard language is used.
DevReferences and DevSearch adapted to this change.
Docu of StdCmds and StdApi updated.

Signed-off-by: Josef Templ <josef.templ@gmail.com>