Fix paragraph in MediaMuxer's javadoc

Originally I meant to fix the "applicaton" typo. Then I saw the width
exceeded 100 columns, and then I noticed that some sentences were
redundant, latin was being used, etc. So I generally reworked the
paragraph. I believe a full javadoc review is due.

Change-Id: I584b844a1083c2b66623fbdff7c8002da2e914ad
Test: Not applicable.