fix Signer UI

[derhuerst]

This PR solves #2704 in the most minimal way: I removed unnecessary CSS, which visually distorted the UI.

The code is still very complex and the styles very brittle, but it is usable again. As the signer will get a lot more features in the next release, a rewrite of some of the components, if not all, will be necessary.

Please check if it is usable for transaction & sign requests, both pending & finished.

edit: Contract deployment requests are broken, addressed in #2759.

[coveralls]

Coverage decreased (-0.03%) to 86.228% when pulling 9a5032c on fix-signer into d2e4baf on master.

[jacogr]

https://gitlab.ethcore.io/Mirrors/ethcore-parity/builds/10625 - js-lint

[coveralls]

Coverage decreased (-0.03%) to 86.096% when pulling f8a0f28 on fix-signer into a1266fc on master.