ENH: Stop automatically collapsing the data probe module
ENH: Improve UI by adding a Push button group box for the Initial step

Also add Icons with it.
ENH: Make the action button bigger by increasing the action text font size
ENH: Always show the help menu when entering the workflow
ENH: Display the save button only once the step is valid
FIX: Preemptively delete volumes in the vessel enhancement step

Not deleting these volume preemptively can lead to a but (no storage node
created) if there is a volume with the same existing in the temp dir.
Merge branch 'workflow'

* workflow:
  FIX: Preemptively delete volumes in the vessel enhancement step
  ENH: Display the save button only once the step is valid
  ENH: Always show the help menu when entering the workflow
  ENH: Make the action button bigger by increasing the action text font size
  ENH: Improve UI by adding a Push button group box for the Initial step
  ENH: Stop automatically collapsing the data probe module
ENH: Display each step help in the module help section

Having a separate widget for displaying help would be confusing and would
crowd the interface. Instead, we can hack the module's help and display
each step help in it.
ENH: Control default settings in vesselview

With this change, we can control the default user settings in the
application without having to modify slicer's code. It works by checking if
a setting file already exists or not. If one already does not exists
already (for example the first time vesselview is started) then the
VesselViewDefaultSettings.ini is used. However if one exists already it's
left intact. It's thus transparent for the user as they can style change
the settings however they want.
FIX: Fix call to observer in ResampleWidget on cancel
ENH: Add Save result text to the save buttons

As a result of this, the tool button were promoted to push buttons.
Note that the "Save results " text as an extra space in the end to provide
a more balanced-looking widget.
ENH: Bigger, greener text for the apply push buttons

In order to make the action more visible/obvious to the user, the push
button were costumized with:
 - a green-colored gradient inspired by the next/before arrows of the
workflow
 - Two spaces before and after the action to enlare the button and
highlight the text
 - an bigger point size (as the application default point size is 12)
FIX: Fix VesselEnhancement step getFileNameFromVolume function
ENH: Finish/Update the VesselExtration step

For this, add another layout that has a 2D view and a 3D view.
ENH: Change label opacity with the foreground opacity
Merge branch 'vesselview-workflow'

* vesselview-workflow:
  ENH: Change label opacity with the foreground opacity
  ENH: Finish/Update the VesselExtration step
  FIX: Fix VesselEnhancement step getFileNameFromVolume function
  ENH: Bigger, greener text for the apply push buttons
  ENH: Add Save result text to the save buttons
  FIX: Fix call to observer in ResampleWidget on cancel
  ENH: Control default settings in vesselview
  ENH: Display each step help in the module help section
  FIX: Preemptively delete volumes in the vessel enhancement step
  ENH: Display the save button only once the step is valid
  ENH: Always show the help menu when entering the workflow
  ENH: Make the action button bigger by increasing the action text font size
  ENH: Improve UI by adding a Push button group box for the Initial step
  ENH: Stop automatically collapsing the data probe module
COMP: Update TubeTK repository address