Fix ctkDICOMobjectListWidget memory leak and other enahancements

* Replaced QSlider with ctkSliderWidget

* Added copy file path to the clipboard.

* changed the order of columns in dicom table to: Tag, Attribute, value, VR, Length

* Double-click on tag table item would open the browser and search the tag in dicomlookup.com

* other stylistic changes and code refactoring.
Fix condition used to unset DICOMApplicationHosting top level option

The variable CTK_PLUGIN_org.commontk.dah.app has been changed
into CTK_PLUGIN_org.commontk.dah.hostedapp.
Added Option for changing tables text density in dicom browser

stylistic changes
Ensure ctk option are considered as superbuild candidate variable.

This fix issue introduced following commit dc70d03 and extend
the functionality of the external project dependency module by
introducing the "_SKIPCACHEVALUE" option.

By setting the variable <varname>_SKIPCACHEVALUE, the system
won't consider the cached value of an option. This is currently needed
in CTK because enabling top level option set the variable in the
current scope without setting the variable in the cache. For that
matter, the value in the current scope should be considered.

Note that the upstream project [1] hosting the external project dependency
macro hasn't yet been updated to support the skip cache value variable.

[1] https://github.com/commontk/Artichoke
Fixed some unused variable warnings

Closes #407
Removed non-functional copy constructor

Fixes #408
Merge branch 'fix-multiple-configure-and-passing-of-options'

* fix-multiple-configure-and-passing-of-options:
  Ensure ctk option are considered as superbuild candidate variable.
  Fix condition used to unset DICOMApplicationHosting top level option
Merge pull request #448 from mehrtash/ctk-dicom-object-list-widget-enhancements

ctkDICOMobjectListWidget enhancements
Merge pull request #438 from mehrtash/3579-very-few-patients-visible-in-DICOM-Browser

Add Combobox for changing the density of dicom table views.
Fix force build for CTK

Replace the 'build depends on always run step' rule for CTK (which does
not work with at least Ninja) with a rule to remove the stamp for the
build step. This more reliably ensures that the build step for CTK is
always executed.
Merge pull request #458 from mwoehlke-kitware/fix-superbuild-ctk-force-build

Fix force build for CTK
Make VTK6 linking more robust

Check for the existence of some libraries and fix underlinked
Debian libs
added repair tool for database and also message box for importin dicom browser

Stylistic changes
Merge pull request #461 from mehrtash/added-repair-tool-and-copy-on-import-message-box

Added repair tool for database and also message box for importing
Fix DCMTK dictionary crashes in plugins

Build it as a shared library in superbuild
Remove duplicates from the include dirs

Having duplicates dramatically increase the command line arguments
that can become close to the maximum limit with ITK and VTK.
Merge branch 'remove-include-duplicates'

* remove-include-duplicates:
  Remove duplicates from the include dirs
Do not link with VTK targets that don't exist
Merge branch 'fix-vtk6-linking'

* fix-vtk6-linking:
  Do not link with VTK targets that don't exist
Don't use set_directory_properties in UseCTK.cmake

It does not do the same as include_directories. Instead, do not add
libraries that already exist.