Make entries configurable

[allyoucanmap]

This PR allows to override entries and paths with the packjson of the project. This is the proposed configuration

{
  ...,
  mapstore: {
    apps: [
      'path/to/dir-of-apps', // scan directory for js or jsx
      'path/to/dir/index.js', // point to a single file
      ['path/to/dir/fileName.js', 'file-name'] // point to a single file and replace the bundle name 
    ],
    html: [
      'path/to/dir-of-ejs', // scan directory for ejs
      'path/to/dir/index.ejs', // point to a single file
      ['path/to/dir/pageName.ejs', 'page-name.html'] // point to a single file and replace the html name
    ],
    themes: [
      'path/to/dir/themes', // scan directory for folder containing theme.less (name from folder)
      'path/to/dir/themes/default', // folder containing theme.less (name from folder)
      'path/to/dir/themes/default/theme.less' // theme.less file to use (name from folder)
    ]
  }
}

All the paths provided in the array of entries are merged in a single object so last entry in the array overrides the previous ones