pages/ext/identifying: multiple updates

* remove timestamps
* update my SASL mechanism list
    * remove ZNC explanations for other mechanisms
        * mention existense of other mechanisms
* mention that newer services don't require SASL to have accountname
    * also mention that they won't be used everywhere in a long time so
    that should be ignored
* Explain SASL EXTERNAL better
* Add link to Limnoria's issue about SASL EXTERNAL.
* Add reminder about earlier mentioned services
* Explain why no to passworded certificates
* HexChat: remove warning about SASL EXTERNAL.
    * Note that it might not work everywhere and HexChat doesn't support
    multiple authentication methods at the same time.
* Remove KiwiIRC link as I didn't get it to work with freenode's
instructions.
* Limnoria: remove network specific certfp.
    * Link to install/upgrade guide and mirror.
* ZNC: add note about missing webadmin.
* Remove warning about giving certfp fingerprint to other people
    * tell that it shouldn't be done, but some servers show it anyway
        * 1 - it's the only thing required to add fingerprint to account
* Fix typos.