Add `target_connection` and `target_file` to Process

[renatomassaro]

Closes #366

Previously there was no way to know what file originated a process, or whether connection_id meant the target connection or the source connection. For most processes that's OK, but not for others. For instance, a FileEncryptProcess has a origin file (the encryptor) and a target file (the file being encrypted). Now there's a way to represent both of them, as well as react to events/signals that affect each one of them.

Same applies to connections. Most or all remote processes have an origin connection (SSH, FTP, CRC) and some of them target a connection (e.g. Encrypting a connection, or Exploiting a connection).

TODO:

• [x] Explicitly name params (connection, file) as either src_* or tgt_*
• [x] Add src_connection_id to FileInstallProcess (SSH connection).

Incidental

• Added tgt_process_id as well, so processes that target other processes have first-class support.

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[sourcelevel-bot[bot]]

Ebert has finished reviewing this Pull Request and has found:

• 3 possible new issues (including those that may have been commented here).
• 3 fixed issues! 🎉

You can see more details about this review at https://ebertapp.io/github/HackerExperience/Helix/pulls/372.

[renatomassaro]

Reviewed 1 of 41 files at r1, 37 of 44 files at r2, 20 of 20 files at r3. Review status: all files reviewed at latest revision, 1 unresolved discussion.

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