Added widget padding

[ppizarror]

Added padding to widgets.
Fixes #229 and #230.

[codecov]

Codecov Report

Merging #236 (7c558b5) into master (5c25049) will increase coverage by 0.21%.
The diff coverage is 85.88%.

@@            Coverage Diff             @@
##           master     #236      +/-   ##
==========================================
+ Coverage   81.76%   81.97%   +0.21%     
==========================================
  Files          44       44              
  Lines        4408     4444      +36     
==========================================
+ Hits         3604     3643      +39     
+ Misses        804      801       -3     

Impacted Files	Coverage Δ
pygame_menu/baseimage.py	82.92% <ø> (ø)
pygame_menu/controls.py	100.00% <ø> (ø)
pygame_menu/events.py	100.00% <ø> (ø)
pygame_menu/examples/__init__.py	100.00% <ø> (ø)
pygame_menu/examples/game_selector.py	87.50% <ø> (-0.13%)	⬇️
pygame_menu/examples/other/__init__.py	100.00% <ø> (ø)
pygame_menu/examples/other/image_background.py	97.14% <ø> (ø)
pygame_menu/examples/scroll_menu.py	92.45% <ø> (ø)
pygame_menu/locals.py	100.00% <ø> (ø)
pygame_menu/scrollarea.py	82.97% <ø> (+2.97%)	⬆️
... and 36 more

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