ScriptService: add API to add & remove script dirs

We want downstream services to have the opportunity to amend the list of
directories from which scripts should be discovered. In particular,
ImageJ's LegacyService will a couple of additional folders for reasons
of backwards compatibility with ImageJ 1.x.

Author: ctrueden

src/main/java/org/scijava/script/DefaultScriptService.java

@@ -133,6 +133,16 @@ public List<File> getScriptDirectories() {
 		return Collections.unmodifiableList(scriptDirs());
 	}
 
+	@Override
+	public void addScriptDirectory(final File scriptDirectory) {
+		scriptDirs().add(scriptDirectory);
+	}
+
+	@Override
+	public void removeScriptDirectory(final File scriptDirectory) {
+		scriptDirs().remove(scriptDirectory);
+	}
+
 	@Override
 	public Collection<ScriptInfo> getScripts() {
 		return Collections.unmodifiableCollection(scripts().values());

src/main/java/org/scijava/script/ScriptService.java

@@ -95,6 +95,12 @@ public interface ScriptService extends SingletonService<ScriptLanguage>,
 	/** Gets the base directories to scan for scripts. */
 	List<File> getScriptDirectories();
 
+	/** Adds a base directory to scan for scripts. */
+	void addScriptDirectory(File scriptDirectory);
+
+	/** Removes a base directory to scan for scripts. */
+	void removeScriptDirectory(File scriptDirectory);
+
 	/** Gets all available scripts. */
 	Collection<ScriptInfo> getScripts();