Version in pom.xml updated to 9.4-SNAPSHOT.

Previously if DataProvidersManagerTest ran before NetworkCrawlerTest it would
set data filters (which are static) that would interfere with
NetworkCrawlerTest. Now both tests clear filters.

Test do not pass yet.

The URL from gitlab cannot be predicted before release. It will be
updated afterwards.

Thanks to Lars Næsbye Christensen for the translations!

Thanks to Roberto Alacevich for the translations.

Conflicts:
	src/main/java/org/orekit/models/earth/ViennaModelCoefficientsLoader.java
	src/test/java/org/orekit/estimation/leastsquares/OrbitDeterminationTest.java
	src/test/java/org/orekit/models/earth/ViennaModelCoefficientsLoaderTest.java

Fixes #498

Thanks to Bryan for the contribution!

Conflicts:
	src/main/java/org/orekit/estimation/measurements/modifiers/RangeRateTroposphericDelayModifier.java
	src/main/java/org/orekit/estimation/measurements/modifiers/RangeTroposphericDelayModifier.java
	src/main/java/org/orekit/models/earth/MariniMurrayModel.java
	src/test/java/org/orekit/estimation/leastsquares/OrbitDeterminationTest.java
	src/test/java/org/orekit/estimation/sequential/KalmanOrbitDeterminationTest.java
	src/test/resources/orbit-determination/GNSS/od_test_GPS07.in
	src/tutorials/java/fr/cs/examples/estimation/OrbitDetermination.java

Conflicts:
	src/main/java/org/orekit/models/earth/MariniMurrayModel.java
	src/test/java/org/orekit/estimation/leastsquares/OrbitDeterminationTest.java
	src/test/resources/orbit-determination/GNSS/od_test_GPS07.in

The previous explanation for multi-threading and propagation set up for
fixing #479 was incomplete. The fact is that propagators cannot be
called from several threads at once (they do preserve some internal
state), but they CAN be used in multi-threaded applications as long as
one propagator is only called from one thread. We even have a helper
class for that: PropagatorsParallelizer.

Fixes #479

Fixes #479

Thanks to Javier for spotting the issue.

Fixes #477

Thanks to Javier for spotting the issue.

Fixes #482

Thanks to Javier for spotting the issue.