[WIP] access routes from email

[kteb]

First try of #1296

I tried quickly the code and it seems working, but I love a review on this one.

And advice where to add the the tests (maybe in default_context_test.go ?

The changes in the mailer are breaking changes, so I think adaption in buffalo fix is needed (it will not stop working, but will not give this functionality to the people who used the old generator).

[codecov]

Codecov Report

Merging #1324 into development will increase coverage by 0.1%.
The diff coverage is 100%.

@@              Coverage Diff               @@
##           development    #1324     +/-   ##
==============================================
+ Coverage        48.23%   48.33%   +0.1%     
==============================================
  Files               90       90             
  Lines             3987     3995      +8     
==============================================
+ Hits              1923     1931      +8     
  Misses            1962     1962             
  Partials           102      102

Impacted Files	Coverage Δ
context.go	100% <100%> (ø)	⬆️

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[kteb]

Better implementation on #1338