Palette extension fix

On extending tl_page palettes, making the :hide attribute optional as for example in Contao 3.2.7 the palette of the "root" page is only {layout_legend} instead of {layout_legend:hide}
ContaoInsertTagFilter

Adding ContaoInsertTagFilter to ThemePlusFilterFactory and fixing ContaoInsertTagFilter class with a public constructor
Merge pull request #75 from ncmsalzburg/PaletteExtensionFix

Palette extension fix
Merge pull request #76 from ncmsalzburg/ContaoInsertTagFilter

ContaoInsertTagFilter
Remove empty line.
Merge branch 'release/4.4'

Conflicts:
	src/Bit3/Contao/ThemePlus/ThemePlus.php
Merge tag '4.4' into develop

Version 4.4