Changes

[495604] Refresh problem on unset hyperlink

The problem was that we ignore the null value in case of an hyperlink.
No when the hyperlink value equals null an empty string is shown in the
UI.

Bug: 495604
Change-Id: I77c0e9fd8ffb6a60deee9f71ec38e617e4da4aeb
Signed-off-by: Mélanie Bats <melanie.bats@obeo.fr>

[498748] Make sure text field changes are applied when switching to
another tab

Bug: 498748
Change-Id: Ied241acb976f8af5461e4aee8ea3abb61ff761f1
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>

[498748] Fix potential NPE when switching back to an existing tab

Tabs are cached according to their descriptors' getId(), which itself
relies (among other things) on the URI of the semantic EObject. That URI
can change when the object is edited (for example: renaming an EClass in
a .ecore). When switching back to a tab previously created (and cached)
with the now-obsolete URI, descriptorToTab.get(descriptor) will return
null, but the code was not ready to handle that case.

Change-Id: I819a0eef62ae6d8e17dbd262c7bccf37a3080c3b
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
Signed-off-by: Stéphane Bégaudeau <stephane.begaudeau@obeo.fr>