[Extension]Load Extension Dependencies in ExtensionsManager

[ryanbogan]

Since the change to SnakeYAML for reading in extensions from extensions.yml, extension dependencies are not being loaded in ExtensionsManager. There is also a test in ExtensionsManagerTests that is not properly checking whether the dependencies are working properly (the test is currently passing).

Steps to fix:

• Add a new constructor in ExtensionsSettings that also takes a list of dependencies and sets the instance variable
• Load the dependencies along with the other fields in readFromExtensionsYml, which is in ExtensionsManager
• Change testDiscover to check if dependencies are loaded