Improve Java client class implementation

[nuest]

The class https://github.com/52North/GEO-label-java/blob/master/client/src/main/java/org/n52/geolabel/client/GeoLabelClientV1.java can be improved so that other users can easily create labels in their Java applications by providing more shortcut methods. Also the URL must be editable (bug).

• remove static URL
• default URL must be configured in constructur (inserted with Guice? from config file?)
• add convenience method createGeoLabelGetUrl(String feedbackUrl)
• add convenience method createGeoLabelGetUrl(String metadataUrl, String feedbackUrl)
• add convenience method createGeoLabelRequest(String metadataUrl, String feedbackUrl)

[hopmann]

The URL is editable, see all createGeoLabelRequest methods. The static URL is the default Service URL.

[nuest]

sorry, my bad - the default should not be set as a static variable though ;-).