[MacPorts] #55906: qgis3: Update to 3.0.0

[MacPorts]

#55906: qgis3: Update to 3.0.0
------------------------+--------------------
 Reporter:  ryandesign  |      Owner:  Veence
     Type:  update      |     Status:  new
 Priority:  Normal      |  Milestone:
Component:  ports       |    Version:
 Keywords:  haspatch    |       Port:  qgis3
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 This patch:

 * updates qgis3 to 3.0.0
 * updates to the `cmake 1.1` portgroup which does out of source builds by
 default, and removes all the code from the portfile that manually did an
 out of source build (see #47197), and removes settings that the cmake
 portgroup sets for you
 * uses the `compiler_blacklist_versions 1.0` portgroup to blacklist clang
 < 500 rather than implementing that manually
 * uses the `cxx11 1.1` portgroup (see #55863) — since qgis 2.x requires
 C++11, I'm assuming qgis 3.x does too
 * adds your GitHub handle to the `maintainers` line
 * removes `use_parallel_build no` and `use_parallel_build yes` lines since
 `yes` is already the default
 * moves `patchfiles` directive to be before the `post-patch` block
 * adds `size` to `checksums`
 * introduces new portfile variable `grass_version` and new patchfile
 placeholder `@GRASS_VERSION@` so that it is no longer necessary to
 manually update the grass version in more than one place (we've forgotten
 to update it in all places before)
 * updates grass version to 7.4.0 in grass variant

 It compiles for me on Sierra and the app launches. I haven't tested more
 than that.

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Ticket URL: <https://trac.macports.org/ticket/55906>
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