port recent changes from polymer-elements

[zoechi]

• [x] #77
• [x] #67
• [x] #92
• [ ] #34
• [ ] #46
• [x] #29
• [ ] #51
• [ ] #50
• [ ] #31
• [ ] #52
• [x] #53
• [ ] #33
• [x] #127
• [x] #128
• [x] #57