First prototype for loading/saving schemas when creating new layer.

- Working for Shapefiles and PostGIS layers.
- Allow from UI save schema and load it from a XML file.
- Add xstream library to parse XML.
- Deploy extcad.jar and libraries to lib (previously, extcad.jar was deployed to parent dir)
Create layer and "save schema" features share the rules the fields must to validate:

- FieldName cannot be void

- FieldName cannot be blank.

- FieldName cannot be longer than the max length provided by the driver (10 for shapefiles; no defined in the case of PostGIS layers).

- FieldName cannot be one of the reserved words. Reserved words are read from file so it's configurable. restricted.txt now provides the list of SQL key words as for PostgreSQL: http://www.postgresql.org/docs/8.4/static/sql-keywords-appendix.html
Improvements on field name validations:

- field name should be a word character. Only one of [a-zA-Z_0-9]
  characters are valid.

- the later and the reserved words validations are checked only when
  saving schemas, not when creating the layer, which is supported by
  gvSIG (it can read and write, for example, shapefiles with special
  characters - so ArcGIS does, but not QGIS). If we want to change
  that behaviour, we should assess how it migth affect to other parts
  of the application.
User-friendly field type in XML file

    By means of a POJO to define the field -FieldDefinition instead of
    FieldDescription provided by gvSIG- we are allowed to store/load in a
    easy way the type of the field as a string.

    I've tested xstream Converters but this approach offered a clear code
    and easier way to marshall/unmarshall the XML.
Show warning if field name contains upper case characters
More validations:

- Ensure fieldName and fieldType are not null.
- fieldName must not be longer than driver capabilities (10 characters
  for Shapefiles) or MAX_FIELD_LENGTH if the latter is not defined.
Catch XML parsing exceptions and show the user a message.
Update translations
Save schema button enabled only if there are rows in table
When saving schema, close table edition to avoid misunderstandings