first phase of source tree restructure

This is the first phase of a big shifting of files and directories
in the source tree.

You will need to run `pip install -e .` before the code will work again!

Here's what's in the current commit:

1) Remove a lot of dead code that dealt with checkpoint and safetensor loading.
2) Entire ckpt_generator hierarchy is now gone!
3) ldm.invoke.generator.*   => invokeai.generator.*
4) ldm.model.*              => invokeai.model.*
5) ldm.invoke.model_manager => invokeai.model.model_manager

6) In addition, a number of frequently-accessed classes can be imported
   from the invokeai.model and invokeai.generator modules:

   from invokeai.generator import ( Generator, PipelineIntermediateState,
                                    StableDiffusionGeneratorPipeline, infill_methods)

   from invokeai.models import ( ModelManager, SDLegacyType
                                 InvokeAIDiffuserComponent, AttentionMapSaver,
                                 DDIMSampler, KSampler, PLMSSampler,
                                 PostprocessingSettings )

invokeai/backend/__init__.py

@@ -3,3 +3,4 @@ Initialization file for invokeai.backend
 '''
 from .invoke_ai_web_server import InvokeAIWebServer
 
+

invokeai/backend/invoke_ai_web_server.py

@@ -27,10 +27,10 @@ from invokeai.backend.modules.parameters import parameters_to_command
 from ldm.generate import Generate
 from ldm.invoke.args import Args, APP_ID, APP_VERSION, calculate_init_img_hash
 from ldm.invoke.conditioning import get_tokens_for_prompt_object, get_prompt_structure, get_tokenizer
-from ldm.invoke.generator.diffusers_pipeline import PipelineIntermediateState
-from ldm.invoke.generator.inpaint import infill_methods
-from ldm.invoke.globals import Globals, global_converted_ckpts_dir
-from ldm.invoke.globals import global_models_dir
+from ..generator import infill_methods, PipelineIntermediateState
+from ldm.invoke.globals import ( Globals, global_converted_ckpts_dir,
+                                 global_models_dir
+                                )
 from ldm.invoke.merge_diffusers import merge_diffusion_models
 from ldm.invoke.pngwriter import PngWriter, retrieve_metadata