Custom theme compilation fails without exclusions on addon

[heutelbeck]

Hello,

When adding

               <dependency>
			<groupId>org.vaadin.addon</groupId>
			<artifactId>confirmdialog</artifactId>
			<version>3.1.1</version>
		</dependency>

To a spring-boot Vaadin 8 project with a custom theme in `src/main/resources/VAADIN' the theme compilation fails:

ERROR] Fehler: Hauptklasse com.vaadin.sass.SassCompiler konnte nicht gefunden oder geladen werden
[ERROR] Compiling theme "VAADIN\themes\apples" failed
org.codehaus.mojo.gwt.shell.JavaCommandException: Command [[
C:\devkit\toolchain\jdk\jre\bin\java -Xmx1G com.vaadin.sass.SassCompiler C:\devkit\workspaces\vaadin8experiment\webinterface\src\main\resources\VAADIN\themes\apples\styles.scss C:\devkit\workspaces\vaadin8experiment\webinterface\src\main\resources\VAADIN\themes\apples\styles.css
]] failed with status 1
	at org.codehaus.mojo.gwt.shell.JavaCommand.execute(JavaCommand.java:330)

Sorry for the German locale. Basically the main class of the SassCompiler cannot be found.

When excluding the vaadin-server dependency of the addon the compilation works again.

               <dependency>
			<groupId>org.vaadin.addon</groupId>
			<artifactId>confirmdialog</artifactId>
			<version>3.1.1</version>
		 	<exclusions>
				<exclusion>
					<groupId>com.vaadin</groupId>
					<artifactId>vaadin-server</artifactId>
				</exclusion>
			</exclusions>
		</dependency>

How to reproduce ?

Try adding the addon to this project: https://github.com/heutelbeck/VaadinUriTemplateNavigation

I actually have no idea what exactly is causing this issue. I at least wanted to document the workaround here if anybody else runs into it.

Thanks for putting the addon together.