Add premailer instead of putting inline styles manually

[amureki]

• make use of https://github.com/peterbe/premailer instead of inlining styles manually into HTML
• move styles to a separate file
• remove voiio-branded colors and styles in favor of the original responsive template
• added a few more blocks, preheader and footer

[amureki]

@codingjoe would love to hear your advice, should we keep premailer as an optional dependency?
If so, I'd need to keep an inlined version of base.html for people who would not want to install it.

[codingjoe]

No, add the dependency. It seems like a solid choice, and I don't feel like maintaining both versions.

[codingjoe]

@amureki the powered by emark thing is funny. Maybe make that a DEBUG=true feature only ;)

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (2f19b6b) 100.00% compared to head (0ed9eb4) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #18   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          168       172    +4     
=========================================
+ Hits           168       172    +4     

Impacted Files	Coverage Δ
emark/message.py	100.00% <100.00%> (ø)

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[amureki]

@codingjoe insightful as always! ✨

[codingjoe]