Changes to Homestead (tutorial) level (v1.07)

This v1.07 update for Keep Defending changes the gameplay for the 1st level "Homestead". As this is the tutorial level for Keep Defending, and so the starting point for all new players, I've expanded its scope a little bit to introduce the management of ally units. To facilitate this I've implemented 2 additional portals (so there are now 4 overall including the player's position) and have enabled crossbow allies for this level. The hint messages displayed in Homestead have been tweaked to show when the player has (a) enough money to buy a teleport, and (b) enough money to buy an ally (crossbow). The hints also disappear automatically after a short time (before this update they remained on until the player accessed the defense interface). Note that there is a setting in the options menu where you can disable all hints permanently if you no longer wish to see them throughout the game. Hopefully the above changes incentivise new players to learn how to manage defenses while playing this (relatively) easy level, before stepping up to the (much more challenging) level "Eagle Heights". Even though the above allows Homestead to be played differently to before, there's no need to reset the leaderboard for this level as the new features are all optional and, if used, actually result in a lower achievable score than before due to enemy kills by allies scoring lower than by the player. Finally, I've also tweaked the projectiles flying overhead in the level selection scene. Cannons are much less frequent (as they are noisy!) whereas the magic bolts are now more frequent. If you experience any bugs or problems with this latest version, or with the game in general, please report them in the group discussions (or comment on this post) and I'll sort them out as quickly as possible! Thanks for supporting and playing Keep Defending!