Remove build folder after plugin is built.
Added local packages support.

Now Package Manager window will have additional switcher between remote and local packages. Local packages will become available whenever path to folder with local packages source codes is specified. This path is saved in Alcatraz settings file, path to local packages is relative.

Details.
1) Added Alcatraz settings file, saved in `kATZPluginsDataDirectory/kATZSettingsFile`.
2) Updated UI:
- added switcher [Remote | Local] that filters table with available packages,
- to Local tab added path selector at the bottom to specify folder with available local packages.
3) Added new fields support in project plist file:
- local package description,
- local package category.
4) Added new property to ATZPackage: `localPath`.
4) Disabled automatic downloading/updating of local packages.
Open folder with package rather then website for local packages.
Open screenshot with name `ATZPluginScreenshot.png` in project root directory if exists for local packages.
Cache package lists and send user notification when packages are available.
Add new filter to package filters: new packages. It is selected by default when new package is added.
Add getters of available (in source codes) and installed plugin versions.
Add version label to table view cell with plugin version information.

For all plugins display label with installed version.
For local plugin if plugin is not installed display label with available version.
Display red label with error if current Xcode UDID is not listed as supported for installed and local plugins.
Rebuild local plugins on every Xcode launch.

Notify user about local plugin being update only if it was outdated (based on installed and available versions).
Use local version of Alcatraz if available instead of fetching from github.
Allow to specify local and remote packages that should be installed automatically when Alcatraz is launched.
Add "Installed" packages filter.
Added support of plugins that are using workspaces to be built.