Added provision for backgroind mask

[gauravkeshre]

There are instances when we need a mask to dim the background when the popup is being displayed.
This can be disabled with properties.

[codecov-io]

Codecov Report

Merging #107 into master will decrease coverage by 0.49%.
The diff coverage is 60.6%.

@@            Coverage Diff            @@
##           master     #107     +/-   ##
=========================================
- Coverage   72.06%   71.57%   -0.5%     
=========================================
  Files           6        6             
  Lines         648      679     +31     
=========================================
+ Hits          467      486     +19     
- Misses        181      193     +12

Impacted Files	Coverage Δ
Source/AMPopTip+Exit.m	17.5% <0%> (-0.93%)	❌
Source/AMPopTipDefaults.h	100% <100%> (ø)	✅
Source/AMPopTip+Entrance.m	34.14% <47.05%> (+2.8%)	✅
Source/AMPopTip.m	84.61% <84.61%> (ø)	✅

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[andreamazz]

Thank you @gauravkeshre
Much appreciated 👍

[andreamazz]

Released with 1.5.0. Note that I set the default value of shouldShowMask to false.