[TOOLS-4532] Migration Wizard Step 4(Schema Mapping Page) improvements

[Srltas]

http://jira.cubrid.org/browse/TOOLS-4532

Purpose
Fix migration wizard step 4(schema mapping page) UI and bug.

1. DB Version word change
   • DB Version -> CUBRID Version
2. Change to show the same as the source schema name instread of "(Enter schema here)" in the target schema input space.
3. Return to Step 3, change the CUBRID version, and chagne the target schema to the changed version when you go to Step 4.

Implementation
N/A

Remarks
N/A