add system tray
Unify proxy setting format

Now all proxy setting is formatted in "{type1:url1, type2:url2}"
url format: ip:port. NO "http" prefix needed.
Add feature: can add twitter account through Settings
set proxy for each account independently
Twitter plugin: getMentionTimeline
mention and comment(retweet instead) added to Twitter plugin
feature added:

Twitter plugin: sendTweet
send tweet through multiple accounts
upgrade plugin interface
bug fix: twitter signature calculation
Twitter plugin: sendRetweet
Twitter plugin: add error handler
improve UE & bug fix

Improve: Add tooltip to guide button
Bug fix: twitter plugin error message analysis
Add module: account_group

Move AccountButton from new_tweet_window.py to account_group.py
account_manager interface changed
feature added: switch user
Add button to switch to all accounts
clear all widget after data retrieved, instead of before