OmeroCpp: Add cmake build system to replace scons

Similar to the bioformats `cmake` support.  To do a test build:

- make a build directory
- cd into the build directory
- run `cmake`.  Use the -G option to specify a specific generator; defaults to `make`, but can use MSVC for Windows builds.  Configure install prefix (`-DCMAKE_PREFIX_PATH=/my/prefix`) as required (or leave as the default).  You might also need to set the include and library paths if they are nonstandard (`CMAKE_INCLUDE_PATH` and `CMAKE_LIBRARY_PATH`).
- run `make` (or `msbuild` or other platform-specific tool)
- run `make install` to install.

Example:
```
export ICE_HOME=/usr/local/share/Ice-3.5
cd components/tools/OmeroCpp
mkdir build
cd build
GTEST_ROOT=/opt/gtest cmake ..
make -j8
make DESTDIR=../install install
```

When the build completes, you should have `libomero-client` in the current working directory and the `utils/chgrp` test program.  If you have `gtest` available, you should also have `test/omero/libomero-test` plus the `test/unit/unit` and `test/integration/integration` executables.

Running the unit+integration tests:
- Set `ICE_CONFIG=/path/to/ice.cfg`
- Create `/path/to/ice.cfg` with the content:

```
omero.host=localhost
omero.user=root
omero.pass=omero
omero.rootpass=omero
```
(modified to suit your configuration)
- run the test programs; you might see transient failures--repeat to check.
- Some of the tests are known to be buggy--this PR does not address this.  I see integration search tests pass on MacOS, some fail on Linux (5 always, 4 intermittent); unit tests pass on MacOS (some intermittent), on Linux 6 RType tests always fail consistently.  These will be fixed separately.  The main test here is that they compile, link and run.  Passing is for later :)

Note:
- The C++ static+generated sources are no longer repackaged as `OMERO.cpp`; you must build in the main source tree.
- Travis now uses `components/tools/travis-build`; see this script for an example of how to build on Ubuntu.  The PR will be green if the `cmake` C++ build and install succeed.
- Jenkins develop C++ jobs will fail due to C++ removal from the `ant` build; this includes all `-all` and `-cpp` targets.  The jobs will require updating once the PR is merged.
- C++ sources and build artifacts are not copied to `/target`; run `make install` to install the headers and libraries.  You can set the prefix path to the target if you want to replicate the existing behaviour.
- A future PR will add proper library versioning, shared_ptr support and other cleanup work; this will use the existing `cmake` support in the bioformats submodule.