updated HTML purifier to 4.5.0
issue #861

Added a place holder and also a small explanation on the admin side
issue / pull reuqest #955 I opted by this more simple solution
Merge pull request #1120 from conejoninja/develop

Develop update
upgrade only the core, do not upgrade themes nor plugins
Merge pull request #1118 from conejoninja/955

issue / pull reuqest #955 I opted by this more simple solution
Merge pull request #1127 from conejoninja/smartupgrade

upgrade only the core, do not upgrade themes nor plugins
Merge pull request #1111 from conejoninja/861

issue #861
Merge pull request #1107 from conejoninja/htmlpurifier

updated HTML purifier to 4.5.0