[TASK] Switch to positive colPos

Since TYPO3 6.2 the install tool has an automated DB schema update function which indiscriminately changes tt_content.colPos to an unsigned integer which has the potential to cause an unrecoverable infinite recursion in the page module when Flux nested content is reset. The field's default type is an unsigned int(11) since TYPO3 6.1 which is our minimum requirement, so we can pretty much choose any new colPos we desire. For example, we could choose the palindromic prime number 18181 because, geek.

The only occurrence in code:

`\FluidTYPO3\Flux\Service\ContentService::COLPOS_FLUXCONTENT`

Tasks:

- [x] Change value of original COLPOS_FLUXCONTENT constant and remove old schema adjust from ext_tables.sql.
- [ ] Enable EM update script to migrate to our newly chosen colPos value.
- [ ] Pick and release this solution to TER in Flux 6.0.3, document the exact SQL query which would migrate all records using one query.
- [ ] Inform in documentation and blog about the URGENT need to execute the EM update script BEFORE updating an existing site to TYPO3 6.2.

There should be zero issues on new 6.2 installs, naturally.