Allow building against the system's Catch library.

Bug: #201
Bug: #178

README.md

@@ -64,7 +64,7 @@ If you've already cloned the repository, you can run `git submodule init && git
   * For older Ubuntu systems (such as Ubuntu 12.04) - you may need to [add some PPAs](https://github.com/powertab/powertabeditor/blob/master/.travis/setup_linux.sh) to get updated versions of the dependencies.
 * Install dependencies:
   * `sudo apt-get update`
-  * `sudo apt-get install cmake qtbase5-dev libboost-dev libboost-date-time-dev libboost-iostreams-dev libboost-program-options-dev libboost-regex-dev libasound2-dev libiberty-dev binutils-dev rapidjson-dev libpugixml-dev`
+  * `sudo apt-get install cmake qtbase5-dev libboost-dev libboost-date-time-dev libboost-iostreams-dev libboost-program-options-dev libboost-regex-dev libasound2-dev libiberty-dev binutils-dev rapidjson-dev libpugixml-dev, catch`
   * `sudo apt-get install timidity` - timidity is not required for building, but is a good sequencer for MIDI playback.
   * Optionally, use [Ninja](http://martine.github.io/ninja/) instead of `make` (`sudo apt-get install ninja-build`)
 * Build:

cmake/third_party/Catch.cmake

@@ -1,6 +1,17 @@
+find_package( Catch )
+
+if ( CATCH_FOUND )
+    set( _catch_dir ${Catch_INCLUDE_DIRS} )
+else ()
+    set( _catch_dir ${PTE_EXTERNAL_DIR}/Catch/single_include )
+    message( STATUS "Using Catch library from ${_catch_dir}" )
+endif ()
+
 add_library( Catch INTERFACE IMPORTED )
 
 set_target_properties(
     Catch PROPERTIES
-    INTERFACE_INCLUDE_DIRECTORIES ${PTE_EXTERNAL_DIR}/Catch/single_include
+    INTERFACE_INCLUDE_DIRECTORIES ${_catch_dir}
 )
+
+unset( _catch_dir )

cmake/third_party/modules/FindCatch.cmake

@@ -0,0 +1,8 @@
+include( FindPackageHandleStandardArgs )
+
+find_path( CATCH_INCLUDE_DIR NAMES catch.hpp)
+set( Catch_INCLUDE_DIRS ${CATCH_INCLUDE_DIR} )
+
+find_package_handle_standard_args( Catch DEFAULT_MSG CATCH_INCLUDE_DIR )
+
+mark_as_advanced( CATCH_INCLUDE_DIR )