Updated tycho plugins

Signed-off-by: Sebastian Hoß <mail@shoss.de>
Updated Clojure BOM.

Use this artifact by importing it into a Clojure POM file as follows:
  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>com.github.sebhoss</groupId>
        <artifactId>clojure-bom</artifactId>
        <version>1.0.0-SNAPSHOT</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>

Signed-off-by: Sebastian Hoß <mail@shoss.de>
Removed redundant .gitignore files.

The .gitignore file inside the parent folder will get picked up by Git
automatically.

Signed-off-by: Sebastian Hoß <mail@shoss.de>
Removed redundant <relativePath />

The default value is already "../pom.xml" so need to specify it
explicitly.

Signed-off-by: Sebastian Hoß <mail@shoss.de>
Updated default configuration for Clojure projects.

This includes the clojure-maven-plugin, and others. Use it by setting it
as a parent for a Clojure project as follows:

  <parent>
    <groupId>com.github.sebhoss</groupId>
    <artifactId>clojure-project</artifactId>
    <version>1.0.0-SNAPSHOT</version>
  </parent>

Signed-off-by: Sebastian Hoß <mail@shoss.de>