Move emergency handlers header file into the support folder.
Refactored signal handling:
- Remove the dependency with the running static variable in the header file.
- Move implementations down to cc files.
- Allow specifying a new signal handler that will be used to stop the applications.
- Move signal handling files to support.
- Import the srslog project into srslte.
- Ported srsue app to use the new logging framework.
- Implemented a wrapper that dispatches log entries to srslog.
- Renamed an existing log test to be more specific to avoid name clashes.