New Table refactors

[zhujinxuan]

1. Use slate-edit-table to support child blocks in table; drop slate-bad-table .
2. Write slate-table-align as a plugin to deal with table alignments
3. Drop slate-text-table. Do not differentiate
4. Refactor API of slate-bind-copy-paste
5. Drop the defaults of slate-bad-table; Only export
   5.1 copy-paste rules
   5.2 align rules

Hopefully I can finish them before Oct.