Added a parser for STK ".e" ephemeris files, modeled after existing parsers like SP3Parser and CPFParser. The file format is documented here.
I added three values to the OrekitMessages enum and had to add corresponding translations to localization files. For one of the messages it was sufficient to copy a message for SP3 files and replace "SP3" by "STK". For the other two I just used <MISSING TRANSLATION> for languages other than English, because I saw that text elsewhere in the localization files.
Fixes #1038 (closed)