Change boundary conditions of neumann GWF ctest.

Remove incompatible dirichlet conditions
(0 and 1 meeting in one corner) for more accurate
testing of the neumann bc.

Add analytical solutions to the input meshes.

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1e0_neumann.prj.md5

-7b04a1ecb48658cd44cacf44e7c12a5f
+1cc471b2c518c4cca9d6e8b2cb000af5

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1e1_neumann.prj.md5

-1d136ab1ffa5ea419e26978ca7d06e80
+ba6948f175bce19a3d8f85e650035f22

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1e2_neumann.prj.md5

-8cae23bf96bc9189a479ab067c17beb0
+00d996c029d050456208d2646cd638b0

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1e3_neumann.prj.md5

-0ee43123514a4920ee069da96473121f
+93897a1fff39d2463545a61420964a4c

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1e4_neumann.prj.md5

-e6c2e2317e153268396e302939fd3c37
+e8b64903064a43af8f5f2dea738f39e8

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1e5_neumann.prj.md5

-f3ff20ea4d49a9dd17ebbdf12e9ff544
+5117ccc4c54e9ce0303c9a7b07611a4b

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1e6_neumann.prj.md5

-e9a7983b85ab94a9cd906072f9b08c1f
+0305e25a33771a4dfc23b17c240f8594

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_1e0.vtu.md5

-93c8c339febcd53c8c72b607488344cd
+42d21af5d700672dbca380b9ff392f16

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_1e1.vtu.md5

-8b72ac29d87bb6821aa87e9a4309bb26
+f1bb40a7d5277976ba8d100929eb2934

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_1e2.vtu.md5

-3efc35c9ad63ae601e676a2b9cfd46ab
+669ad19f5b59718b2c7af5a84a7e2614

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_1e3.vtu.md5

-00dbb657c32d3d0adba6b8d0b0029533
+93edceded9619355818b263d82187254

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_1e4.vtu.md5

-a877ec5ae200505941ea420834f6ff63
+0b0a9a01697178fb60dfabc2ad938006

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_1e5.vtu.md5

-0e002ffca963f4a6b325d7240b11bbe3
+4ea257dd8d96e0ff4f94fd044db1d954

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_1e6.vtu.md5

-c856cd846690f51ac4d90df978989021
+e99f0f0fc59bc5bd0c8e1b5434914d62

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_2e4.vtu.md5

-ebaf6a57027ab2795709a372d15d3a0b
+70f4f50592840a928c81faebc36e3aff

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_3e4.vtu.md5

-7e8ac2cbc317b8728a82feab82d86e5a
+1dd0310e6f7aba9d090e75c31aabb351

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_4e4.vtu.md5

-6e47c3404b9f3ab8b06b5f3d7fc7e9d9
+89ad8065222c9ee63da44f9268a01cea

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_1x1x1_hex_5e4.vtu.md5

-d4220e300ec104839d677c7ebf72c3a3
+ab96fe3dec6516129d2c1318efa9dad5

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_2e4_neumann.prj.md5

-e7dcf3f96b40cb2c3a6c9bb9e3eb67a9
+fc1031d1f25cccd976474c6a033e68b1

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_3e4_neumann.prj.md5

-54c43279079a2b333c9fe89e7668cd86
+cd66611c49e0bf447d5f9a16343b6cdc