left nav sidebar, tom & jerry icons

[Ivshti]

implement a side navigation bar
create vector icons for Tom and Jerry so we have a quick shortcut to those two validators

[alesinka]

[vanina-iv]

A few things here.

1. There is no link to the AdEx home page - this is a must. We have to have it.

2. Let's change AdExplorer to AdEx Explorer - the mix of logo/text just seems weird.

3. The campaign breakdown table has no label - so it will make no sense to a newcomer. Let's add a title or some sort of label saying "Campaigns".

4. Do we have designs for the other pages of the explorer?