Improve source file creator actions

[caendesilva]

Main features:

• Allows custom content to be added when calling the source file creator actions directly.
• Allows custom date to be setwhen calling the post creator action directly.
• Updates the post creator action to use a mockable time helper from Illuminate\Carbon to improve testing

[codecov]

Codecov Report

Merging #1393 (3454d57) into master (0dd4cf1) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             master    #1393     +/-   ##
===========================================
  Coverage     99.97%   99.97%             
- Complexity     1698     3402   +1704     
===========================================
  Files           180      360    +180     
  Lines          4600     9218   +4618     
===========================================
+ Hits           4599     9216   +4617     
- Misses            1        2      +1     

Files	Coverage Δ
...c/Framework/Actions/CreatesNewMarkdownPostFile.php	100.00% <100.00%> (ø)
...src/Framework/Actions/CreatesNewPageSourceFile.php	100.00% <100.00%> (ø)

... and 180 files with indirect coverage changes