Explicitly specify constraint name in create table statement

[apprme]

Exposed uses ALTER TABLE statements to create constraints in case when there are cycles in table structure. In this case it explicitly sets constraint name to fk_${fromCol.table.tableName}_${fromCol.name}_${targetColumn.name}. However, if there are no cycles, constraints are defined in CREATE TABLE statements without name specification: thus, their names are generated by database engine that uses different naming convention (ie Table_ibfk_1 in innodb).

This patch makes Exposed to explicitly specify constraint names in CREATE TABLE statements.

It also sets identifierLengthLimit for MySQL to 64 (as specified here) to fix test that fails otherwise.

[Tapac]

Thank you for your PR, could you please check tests in spring-transaction module?
They start to fail on our CI-server and other tests can't start because of this (https://teamcity.jetbrains.com/viewType.html?buildTypeId=Exposed_PullRequests&branch_Exposed=570%2Fmerge&tab=buildTypeStatusDiv)

[apprme]

apparently it was a missing space character here

sorry for that.