Rework API for SchematicSymbol's libraryIdentifier + libraryName

[mvnmgrx]

As done in #41, add some code to split the libraryIdentifier into its parts:

• Remove token libraryIdentifier
• Add token libraryNickname & entryName
• Add a setter def id() that accepts some string in the following format: <libraryNickname:>entryName and splits it into its parts via regex
• Add a getter def id() that returns the library identifier combined from its parts

Furthermore, it was noticed in #46 that a schematic symbol may have a lib_name token assigned to it. This has nothing to do with the library identifier and may be set depending on the number of variations of a modified library symbol in the schematic.

E.g. when copying a symbol and editing it directly in the schematic, the lib_name token will be set to the symbol's <entryName>_X where X is a unique number that specifies which variation this symbol is of its original.

The following has to be done:

• Add token libraryName