add configuration parameter environmentVariables and skip

I added the paremter "environmentVariables". So I can modify the environment for CasperJS and PhantomJS. I.e. I can run both programs without installation.

Additional I add the "skip" parameter. For a complex maven configuration you need the possibility to deactivate the plugin. 

Example for run tests without installation (here for MaxOS only):

	<profiles>
		<profile>
			<activation>
				<os>
					<family>mac</family>
				</os>
			</activation>
			<properties>
				<skipMac>false</skipMac>
				<skipWindows>true</skipWindows>
				<skipLinux>true</skipLinux>
			</properties>
		</profile>
	</profiles>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-antrun-plugin</artifactId>
				<version>1.7</version>
				<executions>
					<execution>
						<id>unpack-programs</id>
						<phase>pre-integration-test</phase>
						<configuration>
							<skip>${skipMac}</skip>
							<tasks>
								<unzip
									src="${basedir}/src/main/program/n1k0-casperjs-1.1-beta3-0-g4f105a9.zip"
									dest="${project.build.directory}/program" />
								<unzip src="${basedir}/src/main/program/phantomjs-1.9.7-macosx.zip"
									dest="${project.build.directory}/program" />
								<chmod
									file="${project.build.directory}/program/n1k0-casperjs-4f105a9/bin/casperjs"
									perm="u+x" />
								<chmod
									file="${project.build.directory}/program/phantomjs-1.9.7-macosx/bin/phantomjs"
									perm="u+x" />
							</tasks>
						</configuration>
						<goals>
							<goal>run</goal>
						</goals>
					</execution>
				</executions>
			</plugin>

			<plugin>
				<groupId>fr.linsolas</groupId>
				<artifactId>casperjs-runner-maven-plugin</artifactId>
				<version>1.0-RC2</version>
				<configuration>
					<testsPatterns>
						<testsPattern>*.js</testsPattern>
					</testsPatterns>
				</configuration>
				<executions>
					<execution>
						<configuration>
							<skip>${skipMac}</skip>
							<casperExec>${project.build.directory}/program/n1k0-casperjs-4f105a9/bin/casperjs</casperExec>
							<environmentVariables>
								<PATH>${env.PATH}:${project.build.directory}/program/phantomjs-1.9.7-macosx/bin</PATH>
							</environmentVariables>
						</configuration>
						<phase>integration-test</phase>
						<goals>
							<goal>test</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
		</plugins>
	</build>