Support #1375: add demo/image_demo.py support for STARE

[CCODING04]

Motivation

Add STARE dataset demo/image_demo.py support

Modification

mmseg/core/evaluation/class_names.py

def stare_classes():
    """stare class names for external use."""
    return ['background', 'vessel']

def stare_palette():
    """STARE palette for external use"""
    return [[120, 120, 120], [6, 230, 230]]

# dataset_aliases added (omit)

[CLAassistant]

All committers have signed the CLA.

[MengzhangLI]

LGTM except for minor typo.

Please fix the lint error @CCODING04!

[codecov]

Codecov Report

Merging #1376 (ce3d954) into master (17b500f) will decrease coverage by 0.02%.
The diff coverage is 50.00%.

❗ Current head ce3d954 differs from pull request most recent head c200bbf. Consider uploading reports for the commit c200bbf to get more accurate results

@@            Coverage Diff             @@
##           master    #1376      +/-   ##
==========================================
- Coverage   90.42%   90.39%   -0.03%     
==========================================
  Files         133      133              
  Lines        7902     7906       +4     
  Branches     1318     1318              
==========================================
+ Hits         7145     7147       +2     
- Misses        534      536       +2     
  Partials      223      223              

Flag	Coverage Δ
unittests	90.39% <50.00%> (-0.03%)	⬇️

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Impacted Files	Coverage Δ
mmseg/core/evaluation/class_names.py	88.33% <50.00%> (-2.74%)	⬇️

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[CCODING04]

@MengzhangLI
Already taken your advice, thank you 😺