trousers: new package

[Thomas:
 - use a 'select' instead of a 'depends on' for openssl
 - select libiconv when locale support is not available, otherwise the
   build fails due to missing iconv.h
 - disable on BR2_STATIC_LIBS configurations as it doesn't build. It
   could be made to build by patching the trousers Makefile.
 - add missing dependency on thread support in the toolchain
 - add Config.in comment about the thread and dynamic library
   dependencies.
 - add missing <pkg>_LICENSE and <pkg>_LICENSE_FILES variables.]

Signed-off-by: Al West <al.west@v-nova.com>
Signed-off-by: Noé Rubinstein <nrubinstein@aldebaran.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>