Read only installation and multi-user installs

This is a spin-off of #18 (closed) as I think it would be useful to collect information in one place and both topics are actually related. I'll try to update the description as issues/information are collected to have one comprehensive state of affairs. After that this issue might be used to trigger further actions.

Current documentation / state

• General information about launcher arguments: https://help.eclipse.org/latest/topic/org.eclipse.platform.doc.isv/reference/misc/runtime-options.html?cp=2_1_6_0
• How the launcher searches for its library and JVMs: https://help.eclipse.org/latest/topic/org.eclipse.platform.doc.isv/reference/misc/launcher.html?cp=2_1_6_1
• Multi-User Install instructions: https://help.eclipse.org/latest/topic/org.eclipse.platform.doc.isv/reference/misc/multi_user_installs.html?cp=2_1_6_7

Current limitations / improvements

• Updating eclipse.ini not possible in read-only mode: https://github.com/eclipse-equinox/equinox/issues/385
• Eclipse Installer Support for shared/read only installation https://github.com/eclipse-oomph/oomph/issues/34
• Native code should trigger extraction of bundle https://github.com/eclipse-equinox/p2/issues/358