Making sure temporary named file is created with 'w' mode.
Currently, this causes permission error on Windows platform
Merge pull request #621 from NghiaNguyen/master

Making sure temporary named file is created with 'w' mode.
Subtrace data not handled by any importer should be ignored.
Added basic UI for Nestable Async Events

This CL adds basic UI support for nestable async events.
Still need to find out whether the UI looks okay. But right
now it looks like the picture in the design doc below.

Design Doc:
https://docs.google.com/document/d/1Z2uqj59UEts5IiXX78mkdU4kd6e7kE3JUKPoDK97bVs/edit?usp=sharing
addressed comments
added another test case
Incorporated suggestions in parsing rules
a few style fixes
move warning message
updated tests
Merge pull request #616 from kphanee/zip_load_error

 Subtrace data not handled by any importer should be ignored.
addressed comments
Use fixed margins for counter track series spanning the whole viewport
Merge pull request #617 from xunjieli/nestableAsyncUI

Added basic UI for Nestable Async Events
Fixed a typo (changed viewRWorld to viewLWorld)
Merge pull request #626 from petrcermak/clip_fix

Use fixed margins for counter track series spanning the whole viewport
Fix WriteHTMLForTracesToFile
Improve trace2html_unittest
Fix styling
Add gzip file compression back