make getLineWhereCoordAt static
extract line load search method to OneDIntegratorCoreUtils
light improve sample context factories

      + let produce spring's ApplicationContext directly
      + extract protected fillContextSettings
update tb reference
add DoubleHolder
add StablilizedConformingLineIntegratorCore
add OneDPoissonSCSampleContextFactory
add OneDPoissonSCSamplesTest
add StabilizedConformingPolygonVolumeIntegratorCore [semi-finished]

    - lack of the feature of volume force virtual work integration
add TwoDSCRectangleMechanicalSampleContextFactory
extract AbstractSimpJavaConfigContextFactory
move all the context factories into a new sub package
extract ProcessContextConf
tidy 2d mechanical JavaConfig based sample factories

  + rename the classes, remove Rectangle restriction
  + merge all relative config into TwoDMechanicalConf
use decoration for some sample factories