Add a Logger class and associated helpers (e.g. log formatter)

Do incredibly basic work to instantiate logger and pass it to all plugins
Add a "source" to all log events.
Rename Logger to LoggerManager, factor out log entry creation function
into a Logger object, multiple of which can be created by the LoggerMangaer.
Multiple Logger objects feed log entries to a central LoggerManager, where
they are emitted.
Replace some of the console.log statements in generator.js with _logger.log statements
Merge pull request #168 from adobe-photoshop/jrb/logger

Add a Logger class and associated helpers (e.g. log formatter)
Position generated SVG at top left of canvas

Included changes:
Momentarily disable bounds info; fix text position
Also don't fail in keyword substitution if no keys are found.
Move Layer to top left (0,0) while generating SVG
This produces SVG output without the absolute position from the PS
document.  Currently fails for layer groups due to a PS issue
(investigating).
Work around layer bounds bug for groups.
Disable generator tracking during bounds calculation
Must activate the layer to translate coords to 0,0
Add Joel's code for getting the app path.
Fix app path for Mac
Whitespace cleanup (JSHint)
Merge pull request #170 from adobe-photoshop/jp/textpos

Create SVG based on 0,0 position with bounds.
add getPlugin function for use in automation
Merge pull request #173 from adobe-photoshop/jrb/automation

add getPlugin function for use in automation
Merge /Master