Create separate subproject for Dojo envs

[rejuvyesh]

Fixes #36.

I took the path of least resistance in terms of what functions should be part of DojoEnvironments. I also changed how urdf parsing works so that it now assumes that the meshes are located in dirname(pathofurdf)/meshes and appropriately changed the urdf as well. I know it's a big diff, but most stuff should be path changes.

Can fix examples once DojoEnvironments gets registered. Same with benchmarks.

Once merged, should register DojoEnvironments as:

@JuliaRegistrator register subdir=DojoEnvironments

[codecov-commenter]

Codecov Report

Merging #39 (c279641) into main (6c9f8bd) will decrease coverage by 0.11%. The diff coverage is 100.00%.

:exclamation: Current head c279641 differs from pull request most recent head b587b87. Consider uploading reports for the commit b587b87 to get more accurate results

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
- Coverage   91.73%   91.61%   -0.12%     
==========================================
  Files          87       86       -1     
  Lines        4477     4295     -182     
==========================================
- Hits         4107     3935     -172     
+ Misses        370      360      -10     

Impacted Files	Coverage Δ
src/bodies/shapes.jl	88.76% <100.00%> (+0.85%)	:arrow_up:
src/mechanism/urdf.jl	92.05% <100.00%> (-0.32%)	:arrow_down:
src/graph/entry.jl	75.00% <0.00%> (-12.50%)	:arrow_down:
src/contacts/utilities.jl	42.85% <0.00%> (-2.60%)	:arrow_down:
src/gradients/state.jl	88.98% <0.00%> (-0.79%)	:arrow_down:
src/joints/constraints.jl	89.94% <0.00%> (-0.44%)	:arrow_down:
src/mechanism/traversal.jl	95.00% <0.00%> (-0.35%)	:arrow_down:
src/solver/line_search.jl	96.66% <0.00%> (-0.28%)	:arrow_down:
src/graph/system.jl	98.03% <0.00%> (-0.24%)	:arrow_down:
... and 31 more

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[rejuvyesh]

@thowell , @simon-lc: All tests pass and this is ready to be merged. Would definitely recommend carefully reviewing the changes.

[janbruedigam]

@rejuvyesh, thanks a lot for this PR, it's really helpful!