feat(benchmark): add a simple benchmark for the di module

It adds the following tasks to the gulpfile:

1. `benchmarks/clean` // removes the compiled files
2. `benchmarks/build` // compiles all the files in `benchmarks` and creates a benchpress build
3. `benchmarks/run` // fires up a server

It also includes a very simple benchmark. It is not very useful and just serves as an example.

Extra notes:
1. Benchmarks run against the build folder. Right now everything is compiled with type checks enabled. We need to have another task (or maybe a flag) that compiles everything in production mode (without type checks).
This also measures the overhead for calling `System.get`.... But then there is the problem that the module might not have been loaded yet. This can be solved via manual bootstrap of benchpress and using the ES6 module loader polyfill, see below.