Revamp webstart download mechanism

[dizzzz]

Already since a long time eXist-db provides a way to easily start the bundled Java-client: via webstart.
Webstart however, require JAR files to be signed, which makes the eXist-db compile/build process a bit complex, and users often struggle with the signing.

My proposal is to do it a bit different for v5.0:

• have an (optional) XAR file with the signed JAR files - link
• remove the signing steps from the eXist-db build scripts (more easy migration to maven possible)
• simplify the current JNLP/jar download - for OxygenXML compatibility we need -for now- to keep the HTTP connecter, only with a smaller set of UNSIGNED jar files - details

note that for efficiency purposes, the XAR file contains highly-efficient compressed and signed JAR files. for this PACK200 + Gzip is used. We need to add a unpack200 step for compatibility reasons.

My ambition is to have this change as part of eXist-db v5; most of the work is there already. When possible we could Mavenize this XAR project as well, not sure how complex this wil be @adamretter

todo

• remove non-required JARs for download
• remove icon from dashboard
• remove jar signing from scripts

[duncdrum]

anything that reduces build complexity is a win in my book

[adamretter]

@dizzzz in light of the changes to 5.0.0, what is the current thinking on this?

[dizzzz]

Webstart is after java8 EOL ; i am not yet convinced we should spend time here. Maybe a question for the community call?