Beautiful emails (fixes #560)

[Brutus5000]

Add FAF styled emails in MailJet markup language
Load emails at runtime from html templates

[codecov]

Codecov Report

Merging #561 (3bacfa2) into develop (4634a53) will increase coverage by 0.57%.
The diff coverage is 89.85%.

@@              Coverage Diff              @@
##             develop     #561      +/-   ##
=============================================
+ Coverage      75.71%   76.28%   +0.57%     
- Complexity      1124     1169      +45     
=============================================
  Files            240      241       +1     
  Lines           3574     3694     +120     
  Branches         224      231       +7     
=============================================
+ Hits            2706     2818     +112     
- Misses           777      780       +3     
- Partials          91       96       +5     

Impacted Files	Coverage Δ
.../java/com/faforever/api/email/MailBodyBuilder.java	88.52% <88.52%> (ø)
...ain/java/com/faforever/api/email/EmailService.java	100.00% <100.00%> (ø)
.../main/java/com/faforever/api/user/UserService.java	91.94% <100.00%> (ø)
...r/api/config/elide/SpringHibernateTransaction.java	78.57% <0.00%> (-1.43%)	⬇️
.../com/faforever/api/config/FafDatasourceConfig.java	100.00% <0.00%> (ø)
...m/faforever/api/config/LeagueDatasourceConfig.java	100.00% <0.00%> (ø)
...va/com/faforever/api/config/elide/ElideConfig.java	88.88% <0.00%> (+0.88%)	⬆️
...ver/api/config/elide/SpringHibernateDataStore.java	95.91% <0.00%> (+2.81%)	⬆️
...a/com/faforever/api/data/checks/BooleanChange.java	26.66% <0.00%> (+6.66%)	⬆️
...com/faforever/api/data/checks/IsAuthenticated.java	33.33% <0.00%> (+33.33%)	⬆️
... and 2 more

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