Internationalize the UI strings.

Internationalize the UI strings.

	* pom.xml: gwt-maven-plugin: Add the i18n goal and specify a
	<i18nConstantsBundle>, removing the unused <i18nMessagesBundle>.
	* src/main/resources/org/glom/web/client/Messages.properties: Remove this
	because it is unused. Messages are apparently strings that can have
	parameters, but we do not need that yet, so Contants will be enough for now.
	* src/main/java/org/glom/web/OnlineGlom.gwt.xml: Add extend-property lines
	to say that we support the en and de locales.
	* src/main/resources/org/glom/web/client/ui/OnlineGlomConstants.properties:
	The original English strings.
	* src/main/resources/org/glom/web/client/ui/OnlineGlomConstants_de.properties:
	Some German translations of the English strings.
	The i18n goal then uses the .properties file to generate an
	OnlineGlomConstants.java file in target/ and somehow GWT.create() magically
	returns an implementation that returns the translated strings.
	The documentation suggests putting these in src/java/*/client/, but it seems
	best to put it in src/resources/*/client/.
	* src/main/java/org/glom/web/client/ui/TableSelectionViewImpl.java:
	Instantiate OnlineGlomConstants via GWT.create() and use it to get the strings
	instead of hard-coding them.
	Note that we cannot import OnlineGlomConstants because it does not exist yet,
	but that does not seem to stop the build, though it confuses Eclipse.

	You can see the translated string by adding ?locale=de to the URL, like so:
	http://127.0.0.1:8888/OnlineGlom.html?gwt.codesvr=127.0.0.1:9997?locale=de#list:document=film_manager