Feature - Add reusable for attachments

[christophrumpel]

This PR adds the is_reusable key to the attachment payload. By default, it is false but you could activate it like this:

$attachment = new Image('https://laracon.eu/2018/assets/img/speaker_kai.jpg');
$attachment->addExtras('is_reusable', true);

[codecov]

Codecov Report

Merging #75 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master      #75      +/-   ##
============================================
+ Coverage     70.48%   70.51%   +0.03%     
  Complexity      383      383              
============================================
  Files            34       34              
  Lines           952      953       +1     
============================================
+ Hits            671      672       +1     
  Misses          281      281

Impacted Files	Coverage Δ	Complexity Δ
src/FacebookDriver.php	83.15% <100%> (+0.08%)	74 <0> (ø)	⬇️

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