support independently installed modules

Until now Mimosa could load only modules installed with mod:install
command. Since this commit modules installed with 'npm install'
(i.e. "independently installed modules") also supported.

Notes:
* modules installed with mod:install have higher priority
* if Mimosa was installed globally (with 'npm install -g'), then
  it will find only modules installed with 'npm install -g'. If Mimosa
  was installed locally (with 'npm install') then it will find only
  modules installed with 'npm install'
Merge pull request #123 from leonidborisenko/independently-installed-modules

support independently installed modules