new command to list modules.

[TarantoolBot]

tt modules list is a new command to show available modules.
It supports extra flags:

• --version - to show information about module version.
• --path - to show module executables path.

Usage Example:
Get simple list of modules with description.

tt modules list

Can produce output like:

module1 - Description for module1
module2 - Description for module2

Display modules version with executable entry point.

tt modules list --version --path

Possible output:

1.2.3   module1 - modules/modules1/command.sh
v0.0.1  module2 - modules/modules2/main

Requested by @dmyger in tarantool/tt@3ca9d57.