Fix some bugs in multi-patch domains

[yguclu]

• Do not remove sum_factorization argument from auxiliary equation for L2 boundary projection
• Do not use sum factorization for assembly over 3D multi-patch domains (see issue Make DiscreteBilinearForm in psydac.api.fem_bilinear_form work on 3D multi-patch domains #545)
• Make 2D plots work for multi-patch domains
• Set correct multipatch FEM space type on disconnected multipatch domains (fix discretizing a ScalarFunctionSpace on a disconnected multipatch domain returns a VectorFemSpace #552)
• Raise a warning when discretizing a multipatch domain with a periodic flag (fix raise a warning when discretizing a multipatch domain with periodic argument #551)

[codacy-production]

Coverage summary from Codacy

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Coverage variation	Diff coverage
✅ -0.01%	✅ 35.71%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (bb76bb1)	32022	19893	62.12%
Head commit (e3d861b)	64060 (+32038)	39790 (+19897)	62.11% (-0.01%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#546)	14	5	35.71%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[campospinto]

Another (related?) issue is #552 [Edit: should be fixed with this PR]

[yguclu]

@campospinto Thanks for fixing #552! Your one-liner change looks good to me.

As soon as you approve this PR, I think we can merge it

[campospinto]

I added the warning in the function `Geometry.from_topological_domain' to fix issue #551. If the tests pass I will approve the PR

[campospinto]

Good to me now !