Add support for custom maven repositories

[holgerbrandl]

Support for //MVN_REPO declaration.

This will keep kscripts maintainable and self-included. Also, it will allow to provide complex application demos with something like kscript http://short-url

Mockup example using scenery:
https://gist.github.com/holgerbrandl/e2e1b3d4c75f2d8248ea825a07fe26e6

[holgerbrandl]

Attached pom would work for the gist-example

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>kscript</groupId>
    <artifactId>maven_template</artifactId>
    <version>1.0</version>

    <repositories>
        <repository>
            <id>jcenter</id>
            <url>http://jcenter.bintray.com/</url>
        </repository>

        <repository>
            <id>imagej</id>
            <url>http://maven.imagej.net/content/repositories/releases/</url>
        </repository>
    </repositories>

    <dependencies>

        <dependency>
            <groupId>net.clearvolume</groupId>
            <artifactId>cleargl</artifactId>
            <version>2.0.1</version>

        </dependency>

    </dependencies>
</project>