Add support for Meson build system

It's finally happened, a Git module that we care about uses Meson for its build system. This causes kdesrc-build to fail to build the module.

In this case it's telepathy-accounts-signon, see bug 406268.

Current behavior: kdesrc-build encounters telepathy-accounts-signon in the default list of KDE project to build, notices that it can't identify its build system, and aborts the module build.

Desired behavior: kdesrc-build encountered telepathy-accounts-signon (or other Meson-based apps), configures, builds and installs it as normal, everyone moves on with their life.