Move templates into own root level.

[dereuromark]

Solves #1634

The idea:

Template paths are by convention in

• templates/
• besides src/ folder (which is required to detect root path)

Any extensions should follow the same convention or pass their custom path to renderTemplate()

BC Impact:

• BC breaking for all template extensions used in user land code
• Must be outlined in changelogs.

If needed, we could add a shim to lookup also in old "folder" - if not found in new primary location.
This would mitigate the impact.

[codecov-commenter]

Codecov Report

Merging #1848 (5142f55) into master (94069d2) will increase coverage by 0.09%.
The diff coverage is 92.50%.

@@             Coverage Diff              @@
##             master    #1848      +/-   ##
============================================
+ Coverage     87.75%   87.84%   +0.09%     
- Complexity     7761     7771      +10     
============================================
  Files           282      226      -56     
  Lines         21291    21048     -243     
============================================
- Hits          18684    18490     -194     
+ Misses         2607     2558      -49     

Flag	Coverage Δ
5-max	87.84% <92.50%> (+0.09%)	⬆️
7.4	87.84% <92.50%> (+0.09%)	⬆️
agnostic	67.11% <70.00%> (+0.19%)	⬆️
mysql	69.10% <92.50%> (+0.08%)	⬆️
pgsql	69.12% <92.50%> (+0.08%)	⬆️
sqlite	66.93% <92.50%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../Propel/Generator/Builder/Om/AbstractOMBuilder.php	96.91% <80.00%> (+0.01%)	⬆️
src/Propel/Generator/Command/InitCommand.php	69.18% <83.33%> (-0.05%)	⬇️
src/Propel/Common/Util/PathTrait.php	95.23% <95.23%> (ø)
...nerator/Builder/Om/TableMapLoaderScriptBuilder.php	100.00% <100.00%> (ø)
src/Propel/Generator/Manager/MigrationManager.php	95.37% <100.00%> (+0.02%)	⬆️
src/Propel/Generator/Model/Behavior.php	95.06% <100.00%> (+1.31%)	⬆️
...mplates/Behavior/AggregateColumn/objectCompute.php
...emplates/Behavior/AggregateColumn/objectUpdate.php
...s/Behavior/AggregateColumn/objectUpdateRelated.php
...ates/Behavior/AggregateColumn/queryFindRelated.php
... and 53 more

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[dereuromark]

@mringler @nederdirk
What do you think about it? Any concerns or input?

[dereuromark]

I will merge now.
Let me know if we need to enable BC path lookup shim for the beta release - if needed.