Automatic discovery of ADS symbols / channels

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Some of Beckhoff devices based on ADS protocol offers possibility to fetch "symbol table". Symbol table consist name of tag/data point, its type and several other flags. This information can be used to provision channels within discovered and connected PLCs things reducing commisioning time to minimum.

Example symbol table retrieved from TwinCAT/BSD virtual machine running empty PLC program:

      |           PLC4X Field         |          Hex          |                                                            
##### |          Query Syntax         |   Index   |   Offset  |    Type   | Name                                   | Size (B) | Type | Value (type)
------+-------------------------------+-----------+-----------+-----------+----------------------------------------+----------+------|
    0 |           0x4040/0x5dffd:BOOL |    0x4040 |   0x5dffd |      BOOL |Constants.bFPUSupport                   |        1 |   33 | true (java.lang.Boolean)
    2 |           0x4040/0x5dfeb:BOOL |    0x4040 |   0x5dfeb |      BOOL |Constants.bLittleEndian                 |        1 |   33 | true (java.lang.Boolean)
    4 |           0x4040/0x5e002:BOOL |    0x4040 |   0x5e002 |      BOOL |Constants.bMulticoreSupport             |        1 |   33 | false (java.lang.Boolean)
    6 |           0x4040/0x5dffc:BOOL |    0x4040 |   0x5dffc |      BOOL |Constants.bSimulationMode               |        1 |   33 | false (java.lang.Boolean)
    8 |        0x4040/0x5dff4:VERSION |    0x4040 |   0x5dff4 |   VERSION |Constants.CompilerVersion               |        8 |   65 | {uiMajor=3, uiMinor=5, uiServicePack=13, uiPatch=40} (java.util.Map)
   10 |          0x4040/0x5e008:DWORD |    0x4040 |   0x5e008 |     DWORD |Constants.CompilerVersionNumeric        |        4 |   19 | 50662696 (java.lang.Long)
   12 |           0x4040/0x5e000:UINT |    0x4040 |   0x5e000 |      UINT |Constants.nPackMode                     |        2 |   18 | 8 (java.lang.Integer)
   14 |           0x4040/0x5dffe:WORD |    0x4040 |   0x5dffe |      WORD |Constants.nRegisterSize                 |        2 |   18 | 64 (java.lang.Integer)
   16 |        0x4040/0x5dfec:VERSION |    0x4040 |   0x5dfec |   VERSION |Constants.RuntimeVersion                |        8 |   65 | {uiMajor=3, uiMinor=5, uiServicePack=13, uiPatch=0} (java.util.Map)
   18 |          0x4040/0x5e004:DWORD |    0x4040 |   0x5e004 |     DWORD |Constants.RuntimeVersionNumeric         |        4 |   19 | 50662656 (java.lang.Long)

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Completed with 4d837f4.