Implicitly start analysis at a given symbol when only one is provided (i.e. -s flag)

[danmatichuk]

When starting the verifier presents a list of entry points for the user to choose to start the analysis from. Currently that list is populated from any symbols provided via -s and the main entry point defined by the ELF file. To simplify the user interaction we could change it to have the following behavior:

• If no additional symbols are provided, start the analysis from the main ELF entry point
• If exactly one symbol is provided, start the analysis from that symbol
• If more than one symbol is provided, present the list of symbols and allow the user to choose one to start from