Send hover request to all sessions that supports hoverProvider

[predragnikolic]

closes #sublimelsp/LSP-tailwindcss#19

Currently LSP sends only one hover request, which doesn't work nicely when there are multiple sessions running in a file.
LSP should send hover requests to all sessions that supports the hoverProvider.(like we do when requesting completions)

[predragnikolic]

Note: There is one test that was failing even before this change:

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ERROR: test_publish_diagnostics (test_server_notifications.ServerNotifications)
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Traceback (most recent call last):
  File "/home/predragnikolic/.config/sublime-text/Packages/UnitTesting/unittesting/core/py33/case.py", line 28, in _executeTestPart
    yield from deferred
  File "/home/predragnikolic/.config/sublime-text/Packages/LSP/tests/test_server_notifications.py", line 41, in test_publish_diagnostics
    yield lambda: len(self.view.get_regions("lspTESTds3")) > 0
TimeoutError: Condition not fulfilled within 4.00 seconds

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Ran 228 tests in 26.405s