Deprecate integrations

[thelovekesh]

Fixes #403

Tasks Done:

• Add function to show user a warning about integrations deprecation.
• Add @deprecated tags in functions and classes.

Screenshot:

[thelovekesh]

@westonruter I have added @deprecated tags to function/classes and a function to show warnings in the user console as you instructed. Please let me know if this PR needs more improvements.

[codecov-commenter]

Codecov Report

Merging #713 (56b3d8d) into develop (749a985) will decrease coverage by 1.54%.
The diff coverage is 0.00%.

@@              Coverage Diff              @@
##             develop     #713      +/-   ##
=============================================
- Coverage      19.96%   18.41%   -1.55%     
- Complexity       326      334       +8     
=============================================
  Files             56       57       +1     
  Lines           2094     2270     +176     
=============================================
  Hits             418      418              
- Misses          1676     1852     +176     

Flag	Coverage Δ
php	18.41% <0.00%> (-1.55%)	⬇️
unit	18.41% <0.00%> (-1.55%)	⬇️

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Impacted Files	Coverage Δ
...ass-wp-service-worker-admin-assets-integration.php	0.00% <0.00%> (ø)
...tions/class-wp-service-worker-base-integration.php	0.00% <ø> (ø)
...p-service-worker-custom-background-integration.php	0.00% <0.00%> (ø)
...ss-wp-service-worker-custom-header-integration.php	0.00% <0.00%> (ø)
...lass-wp-service-worker-custom-logo-integration.php	0.00% <0.00%> (ø)
...ions/class-wp-service-worker-fonts-integration.php	0.00% <0.00%> (ø)
...ns/class-wp-service-worker-scripts-integration.php	0.00% <0.00%> (ø)
.../class-wp-service-worker-site-icon-integration.php	0.00% <0.00%> (ø)
...ons/class-wp-service-worker-styles-integration.php	0.00% <0.00%> (ø)
integrations/functions.php	0.00% <ø> (ø)
... and 4 more

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