BUG #13889. Fixed arbitrary spacing on the top of properties panel.

Due to vertical spacing provided for the PropertiesFrame's layout, hidden
widgets ended up taking up some space and hence the extra space as one added
more and more sources. This fixes that issue.

Change-Id: Ibc778fb7d86188b7225317a82cd07dec195b4289
Make the Apply button green even when inactive.

Ensure that is Apply is needed, Apply shows up green even if ParaView window
doesn't have focus.

Change-Id: Ic9b2619235f27cba27f4b0a2d1af09b0ead5b26c
BUG #13964: Validate values for double/int properties.

Validate values for double/int properties. Also ditching the funny
pqDoubleEdit. Not sure why it's needed and what purpose it serves.
pqDoubleVectorPropertyWidget now simply uses a QLineEdit with QDoubleValidator.

Change-Id: Ief80c513f3e9fc03ff592f0acf091be61fb24011
BUG #13965. Fixes plethora of panel usability issues.

pqPropertyWidget now fires two signals: changeAvailable() and changeFinished().
pqPropertiesPanel uses changeAvailable() to mark Apply button green, while
changeFinished() to call Apply (if auto-apply is ON) or push the value (for
Display properties). Updated all pqPropertyWidget subclasses to respect this new
protocol. This provides a clean distinction between when widgets say something
is being changed/edited and something has been completely edited and ready to be
processed.

Using pqLineEdit instead of QLineEdit whereever relevant. Since pqLineEdit
provides a textChangedAndEditingFinished() signal that can be used instead of
editingFinished(), we can fire changeFinished() signals more reliable (not
firing unless value was edited by the user) thus avoiding the bogus "Apply" bug.

pqLineEdit also ensures that the most significant digits are always shown.

Change-Id: I0ca10d56577d799791f29ecd7b4fe326064063a9
Merge topic 'misc_panel_fixes' into next

146a6fa BUG #13965. Fixes plethora of panel usability issues.
3f78481 BUG #13964: Validate values for double/int properties.
3233762 Make the Apply button green even when inactive.
fb0f4f9 BUG #13889. Fixed arbitrary spacing on the top of properties panel.