Sort application names to get a sorted algs.txt

Application descriptions are written for each application in OTB_APPLICATIONS_NAME_LIST. This list is unsorted, which results in descriptions written in random order in algs.txt.

In order to get a deterministic output in algs.txt and thus a more reproducible build, make sure to iterate over a sorted list of application names.

See also reproducible-builds.org for context on reproducible builds.