Currently the build without implicitly included precompiled header
is not supported anyway (because Qt MOC source files do not include
stdafx.h, they include plain headers).
So when we decide to support building without implicitly included
precompiled headers we'll have to fix all the headers anyway.
Now base::lambda can be copied and can wrap any immutable lambda.
For mutable lambdas there is base::lambda_once (which you're
supposed to call only once to pass data through lambda captures,
for example by using std::unique_ptr). Generally base::lambda is
passed by value and base::lambda_once is passed by rvalue reference.
Some of MTP::Instance::Private fields access _instance in
destructors. All that cleanup should be performed before the
Instance::~Instance() (which invalidates _private) is called.
If we start logging in and we know, that some of the authorization
keys were read from the hard drive, not generated, we destroy all
the existing authorization keys and start generating new keys.
