Rationalize platform naming

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Tests pass?   | yes
| License       | MIT
| Doc PR        | fridge-project/dbal-docs#4

This PR rationalizes platform naming:

 * Rename `strictMappedType` to `useStrictTypeMapping`
 * Rename `mandatoryTypes` to `customTypes`
 * Pluralize all `support*` methods
 * Rename `getSelectTableCheckSQLQuery` to `getSelectTableChecksSQLQuery` (typo)
 * Check if the transaction isolation is supported before use it
 * Rename `supportInlineTableColumnComments` to `supportInlineColumnComments`
 * Rename all `getSelectTable*` to `getSelect*`
 * Introduce `getAlterTableSQLQuery` which allows to generate any kind of `ALTER TABLE`.

Additionally, it fixes travis conf to avoid random fail...