Get rid from dynamicStyleSheet, fix nested dynamic rules

[lttb]

• use just one stylesheet for static and dynamic values
• use separated rules for static and dynamic values
• resolve https://github.com/cssinjs/styled-jss/issues/23

[coveralls]

Coverage decreased (-2.03%) to 90.678% when pulling bcf7475fee3464ee0f372cb5f2fbd987fccbf08d on feature/nested into ac5cb912242d232841f960be3517460e39f11d1c on master.

[coveralls]

Coverage increased (+4.8%) to 97.479% when pulling 915a4e32559ad94c25e6c27e04bac674b2a5784a on feature/nested into ac5cb912242d232841f960be3517460e39f11d1c on master.

[coveralls]

Coverage increased (+5.6%) to 98.319% when pulling bb9b0c750951703e0459e904ef95251e37c5659a on feature/nested into ac5cb912242d232841f960be3517460e39f11d1c on master.

[coveralls]

Coverage increased (+6.5%) to 99.242% when pulling c223c46ff4bedfb72bdaf8a90d13c5e2ca287ced on feature/nested into ac5cb912242d232841f960be3517460e39f11d1c on master.

[coveralls]

Coverage increased (+6.5%) to 99.231% when pulling ed2edc8d8c2d4a1aef46107d6e731922431fb5df on feature/nested into ac5cb912242d232841f960be3517460e39f11d1c on master.

[coveralls]

Coverage increased (+6.5%) to 99.231% when pulling b4228fbbd93762f08fc99c29aa01239da6e19c6f on feature/nested into ac5cb912242d232841f960be3517460e39f11d1c on master.

[coveralls]

Coverage increased (+6.5%) to 99.231% when pulling b8dde00c4c57a92b357c3d6f3ef2af8bfb9837e5 on feature/nested into ac5cb912242d232841f960be3517460e39f11d1c on master.