properly interpret initial_command as cmdsequence

This ensures the default initial command as given by the
`initial_command` config option will be interpreted as
command*line* as expected, and not as single command.
As a result, one can now use e.g.
  initial_command = search A ; search B

issue: #698
Merge branch '0.3.5-fix-initialcommand-698'
work around new configobj behaviour

regarding utf8 chars in the config being read as str, not unicode
in python v2.7. This pathc introduces an additional
`alot.helper.string_decode` around the translated tagname read from the
config, and fixes issue #693. In the long run, we expect configobj
to be fully backweards compatible.
Merge branch '0.3.5-fix-workaround-new-configobj-693' into testing