Bitcoin Core 0.15.0.1

[laanwj]

Add Bitcoin Core 0.15.0.1.

There's only one bugfix in this release, that affects only GUI users. It was annoying enough to do a new build, though:

After upgrade to 0.15.0, some clients would crash at startup because a custom
fee setting was configured that no longer exists in the GUI. This is a minimal
patch to avoid this issue from occuring.

I've kept the release notes the same as 0.15.0, updating the download link and adding mention of the fix.

[wbnns]

@laanwj Ok, thanks - I'll merge once tests pass.

[wbnns]

@laanwj Hey, apologies, just noticed that it looks like commit 45bdba4 isn't signed - would you mind updating?

[wbnns]

@laanwj Thanks, merging once tests pass. 👍