Add support to redirect the browser if the notification says so.

[jvillafanez]

The action must return an OCS response with a "redirectTo" key in
ocs.data, as well as mark in the action that it wants a redirection,
otherwise the redirection won't happen

Partially requires owncloud/core#32212 (the feature requires it but the app won't break if the core's PR is not there, just the feature won't work)

Fixes #212 along with the core's PR

[codecov-io]

Codecov Report

Merging #218 into master will decrease coverage by 0.41%.
The diff coverage is 62.5%.

@@             Coverage Diff              @@
##             master     #218      +/-   ##
============================================
- Coverage     89.55%   89.13%   -0.42%     
- Complexity      134      138       +4     
============================================
  Files            18       18              
  Lines           536      543       +7     
============================================
+ Hits            480      484       +4     
- Misses           56       59       +3

Flag	Coverage Δ	Complexity Δ
#phpunit	89.13% <62.5%> (-0.42%)	138 <0> (+4)

Impacted Files	Coverage Δ	Complexity Δ
lib/Handler.php	97.88% <60%> (-1.39%)	35 <0> (+3)
lib/Controller/EndpointController.php	93.05% <66.66%> (-1.15%)	18 <0> (+1)

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