[feat] Color deprecation warnings

[vkarak]

Also:

• Move all the warning related parts into a separate file.
• In order to achieve the coloration of the full message, we had to replace the warning formatting method. Also the message is adjusted.

Fixes #1267.

[codecov-io]

Codecov Report

Merging #1549 into master will decrease coverage by 0.16%.
The diff coverage is 58.33%.

@@            Coverage Diff             @@
##           master    #1549      +/-   ##
==========================================
- Coverage   87.94%   87.77%   -0.17%     
==========================================
  Files          43       44       +1     
  Lines        6842     6863      +21     
==========================================
+ Hits         6017     6024       +7     
- Misses        825      839      +14     

Impacted Files	Coverage Δ
reframe/core/deferrable.py	97.51% <ø> (-0.02%)	⬇️
reframe/core/exceptions.py	89.23% <ø> (-0.77%)	⬇️
reframe/core/systems.py	88.31% <0.00%> (ø)
reframe/core/warnings.py	51.72% <51.72%> (ø)
reframe/core/config.py	90.85% <100.00%> (+0.02%)	⬆️
reframe/core/fields.py	98.98% <100.00%> (ø)
reframe/core/meta.py	96.96% <100.00%> (ø)
reframe/core/pipeline.py	92.43% <100.00%> (+0.01%)	⬆️
reframe/frontend/cli.py	79.67% <100.00%> (+0.05%)	⬆️

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[vkarak]

I need to add a unit test to check the formatting of the deprecation warning: https://codecov.io/gh/eth-cscs/reframe/pull/1549/diff?src=pr&el=tree#diff-cmVmcmFtZS9jb3JlL3dhcm5pbmdzLnB5

[vkarak]

@jenkins-cscs retry tsa

[ekouts]

lgtm

[teojgo]

Works fine now.

[vkarak]

@jenkins-cscs retry all