Update and reorganize documentation

- Convert "Common Tasks" to "How-to Guides"
  (QubesOS/qubes-issues#6694)
- Make title capitalization consistent across docs
- Fix leftover h1 headings
- Reorganize various pages and topics
- Update permalinks to better match titles
- Create redirects for changed permalinks
- Miscellaneous cleanup

QubesOS/qubes-issues#6701

user/security-in-qubes/firewall.md

@@ -8,10 +8,9 @@ redirect_from:
 - /doc/QubesFirewall/
 - /wiki/QubesFirewall/
 ref: 166
-title: The Qubes Firewall
+title: Firewall
 ---
 
-
 Understanding firewalling in Qubes
 ----------------------------------
 

user/security-in-qubes/split-gpg.md

@@ -16,8 +16,6 @@ ref: 168
 title: Split GPG
 ---
 
-# Qubes Split GPG
-
 Split GPG implements a concept similar to having a smart card with your private GPG keys, except that the role of the "smart card" is played by another Qubes AppVM.
 This way one not-so-trusted domain, e.g. the one where Thunderbird is running, can delegate all crypto operations -- such as encryption/decryption and signing -- to another, more trusted, network-isolated domain.
 This way the compromise of your domain where Thunderbird or another client app is running -- arguably a not-so-unthinkable scenario -- does not allow the attacker to automatically also steal all your keys.

user/security-in-qubes/u2f-proxy.md

@@ -3,7 +3,7 @@ lang: en
 layout: doc
 permalink: /doc/u2f-proxy/
 ref: 167
-title: The Qubes U2F Proxy
+title: U2F Proxy
 ---
 
 

user/security-in-qubes/yubi-key.md

@@ -1,12 +1,13 @@
 ---
 lang: en
 layout: doc
-permalink: /doc/yubi-key/
+permalink: /doc/yubikey/
 redirect_from:
+- /doc/yubi-key/
 - /en/doc/yubi-key/
 - /doc/YubiKey/
 ref: 169
-title: YubiKey in Qubes
+title: YubiKey
 ---