Added border radius and tightened up the folder boxes. Still needs to have the bottom margin expanded to 8px when in opened state (this needs @torkelo)

* grid: fix small panels migration and make panel height closer to row height

* grid: migrate rows

* grid: increase min panel height

* grid: fix panel placement for complex layouts

* dashboard migration: refactor

* dashboard migration: add tests for grid layout

* dashboard: fix complex layout migration

* dashboard migration fix: fill current row if it possible

* test: fix karma tests by setting default panel span

* dashboard: fix migration when panel height more than row height

* dashboard: fix migration for collapsed rows

* grid: add all rows if even one collapsed or titled row is present

Merge branch 'feat-9932' of https://github.com/alexanderzobnin/grafana into alexanderzobnin-feat-9932