Vectorlabels

This is a prepared version to support labels for the Vector Labels
* everything has been prepared with the exception of the style and the filling and retrieving of a ComboxBox values

SpatialVectorTable
* already had the logic for collection the non-Geometry Fields and setting the first one as the default label
* had a function to retrieve this list [.getLabelList()]
* had a function to retrieve this selected  Field [.getLabelField()]
* a new Function has been added to retrieve, if enabled, the selected field-name [.getSelectedLabelField()]
   * internally it uses i_selected_label_index
     * this is a 1 based index to store the used selected field
        * 1=first field in the list, 2 the second etc
        * if this field value is negative, then the user does not want any label shown
           * the function will return and empty result
        * if this field value is positive, then the user wants a label to be shown
           * the function will return the filed name for the sql query

SpatialiteDatabaseHandler.buildGeometriesInBoundsQuery
* will call table.getSelectedLabelField()
   * if the result is not empty, it will be added AFTER the geometry field to the sql

GeometryIterator
* 2 new functions have been added
   * set_label_text(Stmt stmt)
     * this will empty the 's_label' value
     * if the statement has more than 1 column, it will fill  's_label'
   * get_label_text()
      * will return the value of  's_label', which may be empty
* next()
   * has been adapted to call 'set_label_text(Stmt stmt)' AFTER the geometry has been read

GeopaparazziOverlay.drawFromSpatialite
* has been adapted to call '.get_label_text()'
   * String s_label=geometryIterator.get_label_text();
* a placeholder has been prepared AFTER the geometry has been painted
   * checking if 's_label' is not empty
      * there the label can be painted

?DataPropertiesActivity
* have been adapted to call 
   * getLabelList() from SpatialVectorTable
   * and set a '0' based integer value of the selected field
      * even if the painting of the label is deactivated, the selected field will be retrieved
         * in this way, the last selected field will not be lost if deactivated

TODO:
* add a CheckBox [show label yes/no]
* add a ComboBox with the non-geometry fields of this Table
   * I am assuming that the selecting index of a ComboBox is '0' based
* add to style a '1' based label index
   * i.e. add one to the result
   * if CheckBox is not selected
     * i_selected_label_index*= -1;
* adapt SpatialVectorTable.setStyle
   * replace
     * 'int i_style_selected_label_index=2;'
   * with
     * 'int i_style_selected_label_index=style.i_selected_label_index;'
* add the needed drawing logic in GeopaparazziOverlay.drawFromSpatialite inside the 
   * if (!s_label.equals(""))

With that the logic should be complete.