Meta search 0.3.1

cc @kalxas @rduivenvoorde 

In the same workflow as https://github.com/qgis/QGIS/pull/1350, this PR adds a frozen/stable MetaSearch 0.3.1 from http://plugins.qgis.org/plugins/MetaSearch/version/0.3.1/ via:

```bash
cd python/plugins
lwp-download http://plugins.qgis.org/plugins/MetaSearch/version/0.3.1/download
unzip download.zip
rm -f download.zip
# move python/plugins/MetaSearch/ext-libs/ into python/ext-libs
```
and ties it into the QGIS via `/src/app/qgspluginregistry.cpp` and `python/plugins/CMakeLists.txt`.

I had to manually update some of the dependencies in `python/ext-libs`.

I also added `python/plugins/MetaSearch/CMakeLists.txt`.  Once this is firmed up, I will add this file upstream so management of MetaSearch in QGIS core is simply unzipping the stable release and adding/updating.

Things that can be improved:

- dependency management
- translation

This will become much easier once we move MetaSearch into QGIS proper as per https://github.com/geopython/MetaSearch/issues/62