Switch albumartist_website to XmlNode

Resolves PICARD-593.

Fixes issue with #275 when run from Picard executable under Windows.
Increment version no.
Simplify display_tag_name
Use multi-value %_performance_attributes% ...

... instead of %_performance_live%, etc.

Modifies #285.
Add a test for util.tags.display_tag_name()
Merge pull request #3 from zas/test_display_tag_name

Add a test for util.tags.display_tag_name()
Fix layout (zas comments)

Note: Whilst the previous indentation of "and" was incorrect as per
PEP-8, I think it was actually more readable.
Merge pull request #301 from Sophist-UK/sophist_fix_tag_brackets

Simplify display_tag_name
Handle multiple websites
Persist log view position and size.
Merge pull request #303 from Sophist-UK/sophist_persist_log_status_dialog_size_position

Persist log view position and size.
Fix layouts again (zas comment)
Merge pull request #302 from Sophist-UK/sophist_enhance_#285

Use multi-value %_performance_attributes% ...
Merge pull request #296 from Sophist-UK/sophist_switch_albumartist_website_to_xmlnode

Switch albumartist_website to XmlNode
Add track metadata plugin priority processing

All track metadata processors are equal but some are more equal than
others.

This commit allows a track metadata plugin to register with high
priority, and to run before plugins which are not high priority. This is
needed for the Standardize Performers plugin.
Add Standardise Performers plugin
Add NEWS
Add weight parameter to metadata_processors

Processors having more weight will be run first, default weight is 0.
Set default weights to 50 ...

... so we can have plugins with lower than default priority.
Set default weights to 100...

and plugin weight to 200.