Allow cwd to be configured for build

By default, all paths in the build config (e.g. externs) are assumed to be relative to the ol3 repo root.  To make it so relative paths are resolved from a different directory, use the cwd option.

In addition, this change makes it so the `build.js` task can be run from another directory.
Merge pull request #2275 from tschaub/relative

Allow build task to be run from anywhere and provide option for resolving relative paths.
Merge pull request #2264 from elemoine/object

ol.ObjectAccessor#transform shouldn't dispatch an event to the target object
Document that panning triggers pointermove on touch
Merge pull request #2277 from probins/pm

Document that panning triggers pointermove on touch
Show sketch vertex for all geometry types
Merge pull request #2279 from ahocevar/show-sketch-vertex

Show sketch vertex for all geometry types
Remove libtess.js
Document custom controls
Add tests for ol.coordinate.add().
Add tests for ol.coordinate.createStringXY().
Add tests for ol.coordinate.equals().
Merge pull request #2282 from marcjansen/coordinate-tests

Add more tests to ol.coordinate
Merge pull request #2281 from tschaub/remove-libtess

Remove libtess.js.
Use goog.dom.classlist functions

The goog.dom.classes functions have now been deprecated.  See https://github.com/google/closure-library/commit/97e8a0c0fc7238a56cc4dacd4a96fd4c0735b992
Depends on closure-util version 0.18.0
Fix the closure-library version

The version is the same as the one provided by plovr-81ed862.jar
Merge pull request #2283 from fredj/closure-util.json

Fix the closure-compiler and closure-library versions
Export ol.source.Vector.clear()
Merge pull request #2285 from tsauerwein/vector-source-clear

Export ol.source.Vector.clear()