Update KiCad Symbols with missing descriptions and datasheets from elecena.pl manufacturers data

```tsv
74LS24          
74LS240 Octal Buffer and Line Driver With 3-State Output, active-low enables, inverting outputs http://www.ti.com/lit/ds/symlink/sn74ls240.pdf
74LS241 Octal Buffer and Line Driver With 3-State Output, complementary enables, non-inverting outputs  http://www.ti.com/lit/ds/symlink/sn74ls241.pdf
74LS242 
```