Refactor the mode selection

[rikurauhala]

Currently, setting input and output modes to the same type has been blocked by disabling the selection. This is fine but leads to a degraded user experience.

An example: the user loads the application at 0b.is. By default the modes are set to binary as input and decimal as output. What if the user wants to convert decimal to binary instead? The user opens the input mode select and notices that the decimal option is disabled. The user would have to change the output into something else first.

A possible solution would be to stop disabling options. Instead, if input is set to same as the output, the I/O could be swapped. So in the example case above, the user would simply choose decimal, input would be set to decimal and output would be swapped to binary. There could also be a separate button for swapping the systems in the UI itself.