add tests for insertion, deletion, replacement, moving sections, deleting sections.
add tests for insertion, deletion, replacement, moving sections, deleting sections.

shenhzou654321/DTTableViewManager,KimBin/DTTableViewManager,DenHeadless/DTTableViewManager,shenhzou654321/DTTableViewManager,KimBin/DTTableViewManager,DenHeadless/DTTableViewManager,DenHeadless/DTTableViewManager