Several issues with import/export for PCR library

1. The "Import Primers" dialog is inconsistent. It allows selecting primers from both local FS and a shared DB, but imports them from only one of these sources.
2. The "Export primers" dialog should have consistent result path separators. On Windows default path contains both slashes and back slashes.
3. The layout of the "Export primers" dialog is slightly incorrect. See the attached screenshots.
4. If primers are exported to a shared DB the destination path line edit can change its color in case of an incorrect path. But this check is done only when user hits "OK". The user input should be evaluated on each path modification and the line edit has to change its color if necessary.
5. No error message appears if a user sets wrong shared DB path during primers export and presses "OK". The line edit color change isn't sufficient.
6. The "OK" button in the export dialog should be renamed to "Export".