Allow initialization of an attitude provider from an attitude segment.

src/changes/changes.xml

src/main/java/org/orekit/files/ccsds/AEMAttitudeType.java

src/main/java/org/orekit/files/ccsds/AEMFile.java

src/main/java/org/orekit/files/ccsds/AEMParser.java

.../java/org/orekit/files/general/AttitudeEphemerisFile.java

...org/orekit/files/general/OrekitAttitudeEphemerisFile.java

...test/java/org/orekit/files/ccsds/AEMAttitudeTypeTest.java

src/test/java/org/orekit/files/ccsds/AEMParserTest.java

...orekit/files/general/OrekitAttitudeEphemerisFileTest.java

src/test/resources/ccsds/AEMExample8.txt

src/test/resources/ccsds/AEMExample9.txt