Implement latest requested PR changes

[dbutt-scottlogic]

1. Tests which handle FDC3 errors are assuming that they are strings (this is how Finsemble raises them, but is wrong). So instead of (for example) ex !== ResolveError.NoAppsFound we should have ex.message !== ResolveError.NoAppsFound.
   a. fdc3.findIntent.ts
   b. fdc3.findIntentsByContext.ts
   c. fdc3.open.ts
   d. fdc3.raiseIntent.ts
   e. fdc3.raiseIntentForContext.ts
2. Move the appDefinition.json file out of the src dir and into the root of the project and update the README.md to match.
3. Where the tests themselves raise exceptions, these should be raised as Errors not strings, i.e. throw new Error(ExpectedErrorNotThrownError);
   a. fdc3.joinChannel.ts
   b. fdc3.open.ts
   c. fdc3.findIntentsByContext.ts
   d. fdc3.raiseIntent.ts
   e. fdc3.raiseIntentForContext.ts
4. The icon in appdefinition.json could the changed to the icon http://fdc3.finos.org/toolbox/fdc3-workbench/fdc3-icon-256.png (copy it into the project).