[Feature][QGIS-Server] Specifying url for QgsComposerHtml in GetPRint Request

The idea is to add the capability to specify an URL to a QgsComposerHtml
element in the GetPrint request.
This will give the ability to get PDF with content base on a web
service.
dont translate names in customization tree, fixes #8039
When scale bar is numeric disable controls which don't apply
Don't change scale bar box size automatically when style is numeric
Remove duplicate call to adjustBoxSize when scale bar font changes
Also disable color buttons which don't apply for numeric scale bars
Make numeric scale bars respect font color and alignment settings (fix #7830)
set min updateThreshold to 1000
Slovak translation update.
Merge pull request #654 from imincik/slovak

Slovak translation update.
Fix for #8052, QGIS 2.0 does not respect labels' scale-based visibility in projects from previous version

- Also fix long standing unreported bug where scales closer than 1:1, e.g. 5:1, could not be set
fix #8060 (new SIP API)