[ADAM-993] Support loading files using globs and from directory paths.

Resolves #993.

* Add private helper functions in ADAMContext to elaborate out globs and
  directory paths when loading files.
* Eliminate unused functions for elaborating paths and loading mixtures
  of read files, and some redundant dictionary loading functions.
* Add tests to cover loading directories/globs of:
  * Parquet files
  * BAM files (with/without using indices)
  * VCF files

adam-cli/src/main/scala/org/bdgenomics/adam/cli/ListDict.scala

@@ -43,12 +43,8 @@ class ListDict(protected val args: ListDictArgs) extends BDGSparkCommand[ListDic
   val companion: BDGCommandCompanion = ListDict
 
   def run(sc: SparkContext): Unit = {
-    val dict = sc.loadDictionary[AlignmentRecord](args.inputPath)
+    val gRdd = sc.loadAlignments(args.inputPath)
 
-    dict.records.foreach {
-      rec: SequenceRecord =>
-        println("%s\t%d".format(rec.name, rec.length))
-    }
+    println(gRdd.sequences)
   }
-
 }