Mailbox: add renaming capability

[OmarMonterrey]

I'm new to open-source colaborating, so I'm sorry if I did something wrong. This pull request is related to Issue #446 (Mailbox renaming feature request)

[codecov[bot]]

Codecov Report

Merging #540 (8913ee1) into master (4e2980c) will increase coverage by 0.05%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #540      +/-   ##
============================================
+ Coverage     95.52%   95.57%   +0.05%     
- Complexity      354      356       +2     
============================================
  Files            45       45              
  Lines           826      837      +11     
============================================
+ Hits            789      800      +11     
  Misses           37       37              

Impacted Files	Coverage Δ
src/Mailbox.php	97.11% <100.00%> (+0.34%)	:arrow_up:

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[Slamdunk]

I've just pushed to master few changes to make local build easier and fix issues non related to this very PR, so please rebase before next developments.

[Slamdunk]

Hi, can you also add tests please?

[OmarMonterrey]

Sorry I didn't took into account the encoding of the names, I fixed it for the tests to properly pass.

[Slamdunk]

Thank you @OmarMonterrey