Do not check for updates if libman.json file is missing

Check the libman.json file exists before checking for updates. Fixes
error logged due to a null filename being used for the libman.json
file when checking for updates.

Could not get Library Manager updates for ''
System.ArgumentNullException: Value cannot be null. (Parameter 'key')
   at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
   at System.Collections.Generic.Dictionary`2.ContainsKey(TKey key)
   at Microsoft.Web.LibraryManager.Vsix.Contracts.DependenciesFactory.FromConfigFile(String configFilePath)
   at MonoDevelop.LibraryManager.Updates.UpdatedLibrariesService.GetUpdatesAsync(FilePath configFilePath, CancellationToken cancellationToken)
   at MonoDevelop.LibraryManager.Updates.UpdatedLibrariesService.SafeGetUpdatesAsync(FilePath configFilePath, CancellationToken cancellationToken)

Update addin version to 0.3

Fix Add Client-Side Library dialog not opening in VS Mac 8.8

VS Mac 8.8's SolutionPad API has changed. SolutionPad.TreeView no
longer exists. It is replaced with SolutionPad.Controller.

Fixes #1

Restore when libman.json file saved

Added a document controller extension that checks whether there are
any errors on opening the libman.json and on saving. Errors are
reported in the text editor and to the Errors list. On saving the
libman.json file a restore is run.

Change Provider APIs to use name and version instead of libraryId

- Separates the data objects from Manifest and LibraryInstallationState
- Remove libraryId from from ILibraryInstallationState
- Adapt all clients and use cases to use name and version instead of
libraryId
- Fix all tests to use name and version instead of libraryId

Close dialog when install button is clicked