Release notes and version for v0.9.11

[kristapsk]

Please review and test. Treat this as a release candidate. :)

[MarnixCroes]

lgtm, few nits

[AdamISZ]

LGTM at dd462a6

Though it's outside the norm, it would not be unreasonable to shout out @whitslack specifically for an extremely significant contribution here (in the section on wallet performance). Whatever you think, it's not a huge deal.
A vaguely related point: the description of how wallet syncing performance has improved is good, but I'm wondering if we could add this point (because it's such a common, big, problem for users): that if they are syncing a heavily used wallet from a seedphrase on a new Core instance, they can now use a large -g gaplimit and it will take far less time than it did before. I think your description of the ability to disable caching is fine. Another thing you could mention (maybe?) is that the size of the *.jmdat files will be larger than before, and that this is normal, because it contains cached data (but still encrypted).

[kristapsk]

Addressed review comments by @MarnixCroes and @AdamISZ.

Though it's outside the norm, it would not be unreasonable to shout out @whitslack specifically for an extremely significant contribution here (in the section on wallet performance).

Added that to "Credits" section. Also mentioned new first time contributors.

[AdamISZ]

ACK 053e9d8

[MarnixCroes]

ack 053e9d8