Add option to suppress errors related to missing property sets

[lwrage]

Summary

Models that depend on a contributed property set will have errors if the contributing plugin is not installed.
It should be configurable to suppress such errors.

Optionally allow the user to enter names of property sets to ignore.

Environment

• OSATE Version: 2.8.0
• Operating System: all

[asazonova]

Discussed requirements:

• New preference page per workspace only, where user can type in the names of property sets to be ignored
• Suppress the errors - TBD

[asazonova]

add a field to the preferences where the user can set whether to report a warning or completely ignore the listed property sets

suppress the errors => error message customization for Xtext linking