Prop344: Update and Categorize Vectors; Ground in Threat Model

I've re-grounded the entire proposal in Tor's OG Design Doc Threat Model language, and provide a background of this threat model as part of the introduction, to help new folks get up to speed and better conceptualize this proposal.

The proposal has been updated to classify all vectors into the following three categories:

1. Internal Covert Channels
2. Behavior Manipulation
3. Augmented Observation

It now also proposes that Tor's threat model be expanded to explicitly cover these categories. These categories (and their vectors) were either explicitly excluded, or in an ambigous status before.

Additionally, the following vectors have been added:

• Guard Trapper Attacks
• Relay DoS/OOM

The following examples have been added to existing vectors

• Path restriction problems
• .exit notation
• Exit Policy abuse by websites+exits
• circuit dirtyness abuse by exits
• Dropped cells types unique to onion services

proposals/000-index.txt

@@ -265,7 +265,7 @@ Proposals by number:
 341  A better algorithm for out-of-sockets eviction [OPEN]
 342  Decoupling hs_interval and SRV lifetime [DRAFT]
 343  CAA Extensions for the Tor Rendezvous Specification [OPEN]
-344  Prioritizing Protocol Information Leaks in Tor [OPEN]
+344  Information Leak Hazards for Tor Implementations [OPEN]
 345  Migrating the tor specifications to mdbook [CLOSED]
 346  Clarifying and extending the use of protocol versioning [OPEN]
 347  Domain separation for certificate signing keys [OPEN]
@@ -313,7 +313,7 @@ Proposals by status:
    340  Packed and fragmented relay messages
    341  A better algorithm for out-of-sockets eviction
    343  CAA Extensions for the Tor Rendezvous Specification
-   344  Prioritizing Protocol Information Leaks in Tor
+   344  Information Leak Hazards for Tor Implementations
    346  Clarifying and extending the use of protocol versioning
    347  Domain separation for certificate signing keys
    348  UDP Application Support in Tor