Global review of error messages to make them more understandable

[bertfrees]

• [done] Move to a single mechanism for messaging that can be used from Java, XSLT and XProc
• [done] Support for progress messages in GUI, incl. indentation
• [doing] Fix warnings (esp. those that look like errors)
• Revisit how progress messages work: Progress messages system overhaul #102
  • make indentation depth vs. log level play nicely together
  • possibly update messages API
  • make more implicit
• Handle or ignore progress messages in CLI
• Handle or ignore progress messages in GUI
• Make it obvious that (XProc or Java) runtime errors are runtime errors
• Make it easier to locate errors (XProc stack trace etc.)

Related issues:

• jul-to-slf4j bridge pipeline-assembly#87
• Fix logging related errors pipeline-assembly#104
• Fix XSLT warnings that looks like errors pipeline-mod-braille#38
• More useful feedback from validation in dotify:xml-to-obfl pipeline-mod-braille#89
• Proper logging pipeline-mod-braille#19
• Ability to send messages to the execution log from Java pipeline#477
• px:message: move to new mechanism for messaging pipeline-modules-common#92
• Messages with severity="DEBUG" are not output through the Web API pipeline-modules-common#88
• Message severity from XSLT messages pipeline#476
• Progress indicator for jobs pipeline#445
• Make the messages from the server look prettier pipeline#155
• Handle progress messages pipeline-cli-go#12
• Proper exception handling in XProc pipeline-mod-braille#18
• Generalize job status "VALIDATION_FAIL" to "FAIL" pipeline-framework#121
• More useful execution log output snaekobbi/issues#29
• don't use severity=INFO for messages in tts-utils pipeline-mod-tts#53

See branches:

• daisy/framework@job-messages-java
• daisy/pipeline-mod-braille@develop...messages

[bertfrees]

Also related: daisy/xmlcalabash1@eedce13