Decrease ambiguity in column_view.c typedef

Rename `struct column_t` to `struct columns_list_t`.

Suggested by cppcheck.
Merge branch 'cppcheck-fixes'
Add check for a NULL pointer to command_cmd()

Suggested by clang checker.
Define a macro for max cmdline command name length

Less magic numbers!
Fix possible one byte stack array overflow

Suggested by clang static analyser.
Initialize multi field of the key_info_t structure

Also made code in remove_user_keys() and find_user_keys() a bit better.

Suggested by clang static analyzer.
Merge branch 'clang-checker-fixes'