fix ExtensionTest::testGenericExtensionMetaInformation which was testing only xhprof
be tolerant with extensions that have no config[0-9]?.m4 file, pass tests again
com_dotnet is only known extension that has no config[0-9]?.m4 file right now
Refactoring extension known / install codes. and NOW also support bitbucket.

Signed-off-by: Rack Lin <racklin@gmail.com>
Refactoring the Extensin\Hosting interface to Extension\Provider, Added `provider` key to extensions.json file, so every Provider should use the same file.

Signed-off-by: Rack Lin <racklin@gmail.com>
Added supports simple DSL extension name for `provider:user/package` and `provider@user/package` forms.

Signed-off-by: Rack Lin <racklin@gmail.com>
added unit-test for Extension Known.

Signed-off-by: Rack Lin <racklin@gmail.com>
Remove extensions.json and its associate methods temporarily.

Signed-off-by: Rack Lin <racklin@gmail.com>